Maîtriser la programmation Python : guide de programmation amusant et facile pour les débutants

1. Welcome: Hey, there. I hope your day is going fantastic, and together, let's make it more enjoyable. I'm not going to ask you formality questions like, how are you and all. I already know you're doing great. After all, you have dared to learn something new today, and that takes a good mood, right? Otherwise, you would have been binge watching cat videos or scrolling through memes right now. Anyway, welcome to the Python world. You need not to fear in this world because here the snake or the language that has got its name from the snake is very friendly. You have just tapped into the world where coding is easy, fun, and feels less like learning a new language and more like solving a fun puzzle. First off, give yourself a pat on your back because simple, I cannot do so for you. Okay, do so for deciding to learn Python. Python is very sweet, and this journey is going to take you from I have never coded in my life. I know Python coding very well. This course will lay down a solid foundation of knowledge in Python. You may ask, What shall I do with that foundation? Whatever you want, that is up to you. Python is common foundation for various domains. You can use it for multiple purpose, web development, data analysis, machine learning, automating tasks, building games, you name it. Python has got it covered. And the best part, it is easy and beginner friendly. You won't need a computer science degree or a brain the size of the moon to get started. It is easy to read, easy to write, and it forgives your mistakes. It is like the chillst teacher you have ever had. No matter what your career goal is, Python welcomes you with open parenthesis. If you have the thirst for the knowledge, this course will guide you to the lake of Python. Remember, we can only lead you there. We can't make you to drink. It is up to you to consume this knowledge. But how? Just follow three step process, practice, experiment, and apply, and that's it. Promise me you follow these three process. Not just for programming, you can follow these steps to learn almost any skills. But if I have to make that statement, I have to give a quick disclaimer for my safety. Don't experiment if you are a doctor or a pilot unless you like living on the edge. Do so at your own risk. I'm not responsible for any consequences. I hope it is clear. Let us come back to the world of Python. By the end of this course, you will not only speaking Python fluently, you will also be writing it. The best part is you will enjoy the learning process. Are you excited? Give me a virtual hi fi, but be careful. Please don't knock your computer while doing it. You're still half asleep, raise your virtual coffee mug, but no promises it will wake you up. Are you ready to start your Python adventure, gather some snacks? Let us dive in together, have some fun and write some de, trust me, it's going to be awesome. 2. Introduction to Python: Welcome back. In this session, we are going to cover everything you need to know about Python. It is important to know about our new friend before we go forward together. Python has become so popular in the recent years. What is Python? Why it is so popular? It is the time to answer this question. Python is open source, high level general purpose programming language. I know a lot of new words that doesn't make it cool. As I promised, let us break it into small consumable bites. Let us understand what is open source. Have you ever planned potluck party with your friends where instead of one person cooking everything, everyone brings a dish. Now, here is the cool part about it. Not just you all get to eat the variety of delicious food, but everyone also shares their recipes. Want to add some extra spice to the curry. Go ahead. Think the cake could use more frosting. Why not? You can tweak, change, and improve every dish as you like. That is exactly how Python or any open source tool works. It is like software that is a potluck of code. The recipe or the source code is publicly available. Shared with everyone, and you can modify it, improve it, or even mix it with your own secret sauce. The best part, you can eat or use it for free. And being community driven, anyone can take the responsibility to make it a better one. That is how Python is getting better and feature rich. So first term, open source is digested. The term general purpose programming language is very straightforward. It means the language is not specialized for any specific domains, but is designed to solve variety of problems and can be used for wide range of applications. As we discussed in the beginning, Python could be used for variety of applications ranging from software development to analyzing the data. Python is among the general purpose programming language. Then what do the term high level language mean? Is it talking about the social status of the language? No. But to understand that, we must know the different level of programming languages. The early generation computers used to understand only the binary language just composed of zeros and ones. That is the native language that computers speak fluently and understand better. This language is also called as machine language. Even the programmer is supposed to communicate with the computers through this alien machine language full of zeros and ones. It is super efficient for computer to understand and process. But what about us? Let us be real. If we had to talk to computers in just zeros and ones, we would all be crying within 5 minutes. Unless you enjoy typing out long strings of zeros and ones just to say hello world. It is not practical for us humans. Imagine, we need to program the softwares and complex calculations using that strange language. Just imagination would make me feel horrible. Then how about it in actions? To resolve that, programming languages are developed that can be easily programmed by the humans. All modern applications are developed using the programming languages. These languages can be classified into low level languages and high level languages. Popular low level languages are CC plus plus and Fortran. C plus plus is arguable because it can be both low and high level and hence it is called mid level language. These low level languages are closer to what computer understands, but they give you a bit more control. Think of them as the manual transmission of programming. You get more control over the car, I mean, computer, but you have got to do all the hard work yourself, like managing memory and processes. Low level languages are great when you need speed and control. But let us be honest. They're not always the most fun or beginner friendly. Then we have the high level languages like our buddy Python. These are designed to be more like us, human readable, easy to learn, and very forgiving. High level languages are like using smartphone app, simple interface, and no need to worry about what is happening under the hood. Even among the members of high level languages, Python is one of the easiest and beginner friendly language. If you can understand plain English, you can understand Python. Python is known for its simple English like syntax. If you understand me right now, you are already halfway there. Python is so easy that even your pet could understand it if your pet had advanced cognitive abilities, of course. Don't blame me later if your pet doesn't become the next coding prodigy. And also how many times have you heard Life is short? Yes, it is the hard truth of the life. Then why waste precious time writing long convoluted code when Python can do it in fewer lines. Python simplicity saves your time, effort, and possibly a few stands of your hair. Most Python programs are written with at least 30% fewer lines of code compared to other popular languages like C plus plus and Java. But that doesn't mean the computers of present day has forgot its native binary language. Even the modern computers use the machine language. But it is restricted to process the information and to communicate with each other fellow machines. That is obvious. We all have some native language or some call it as mother tongue, the language that our parents used to speak at home. When we think when we speak at home, we use our native language because every cell of our body understand language. When we grow, we learn other languages as per our need. But our brain first translates the new language into native language to understand. That is very common. That is exactly how computer works. When computer thinks or process the data and talk with other computer, it always use binary language. When we program using any programming language, computer translate it into machine language and then process it. Hence, high level languages consume more time to process than low level languages, and machine language take least time to process as it is the native language of computers. I hope the machine language, low level language, and high level language is processed properly in your brain. Apart from being easy, beginner friendly and least number of lines, there are many other reasons to love Python. Well, Python is like the Swiss Army knife of programming languages. Super versatile, easy to use, and it can handle just about anything you throw at it. Here are a few reasons why choosing Python is a genius move. The first reason, Python is versatile and it is cross platform. Python is like water. It fits into any container. It works across all major operating systems, whether you're coding on Windows, Mac, or even Linux. Python works on all of them like a charm. It is like that one friend who gets along with everyone at a party, and you can use it for the projects in various domains without breaking a sweat. Second reason, Python has a library of libraries, thousands of them. For any domain you are interested in, there are likely a library or several to help you out. Data science, web development, artificial intelligence, you name it. Python has a bunch of libraries to solve them. If you don't know about the libraries, it is pre coded resources help you to solve the complex problems. Think of Python libraries like the bunch of pre coded tools. You can just grab off the shelf. The real challenge about the Python library is choosing the right one from all the options available for you. Do you need another reason to love Python? Python has massive community. You get friends, not for parting, but they share common interest, who would help you in programming journey. Need help stuck with the problem, and trust me, it will happen while programming. Chances are, someone else has faced the same problem too. They might have got some error as you do, and guess what? They have already solved it and posted the answer online. Just type your problem or error into Google, and there is a good chance someone has already explained how to tackle the problem or error in some platform like stack Oflow. You are never alone in your Python journey. And what if you want friends for a party? Well, that's another story. But you can count me in always anytime. With so many reasons in favor, Python is really attempting language to learn. But before you start thinking, Python is perfect. Let me be real with you. Like all the good things, it has few setbacks. First up, Python is little slow, not slow like a turtois, but compared to faster languages like C plus plus, Python takes its time. But for most of the programs, this delay is not even noticeable. When you are coding heavy video games and heavy processing back ends of a software, you may realize Python is bit slower, but you have saved a lot of time while programming. There are few areas where Python is not the good fit. The first thing is mobile application development. If you are dreaming of building the next big mobile app, Python might not be a GT. It is fantastic for backend stuff, but for mobile, it is not the best. Another area where Python is not a good option is front end development. If you're wondering what this front end development is, front end is the interface of any software that is visible for the user. Back end is all those things like calculations, interacting with the servers that is happening behind the scene under the hood and not at all visible to the user. Python is good at back end development, but not for the front end development. But hey, these small issues are like finding a tiny scratch on the shining surface. Let us celebrate Python for what it is, not what it is not. And that is why Python is used by many top companies and organizations. Ever wonder how Netflix know what you want to watch next? Yes, they are using Python. To sum it up, Python is like the superhero of programming languages, flexible, powerful, and easy to learn. Whether you want to automate boring task, build websites, or dive into data science, Python has got you covered, and that I hope makes you know everything that you are supposed to know about Python. After the good introduction, we can start our journey officially with Python. See you soon. 3. Programming Interface: Now I will give you a simple and easy task. Look at these hairless and earless people and recognize their profession. It is a very easy task, right? You hardly need seconds to answer it. Okay. Done. I have a few questions for you now. Do you know these people before? Are they your neighbors or do you meet them regularly? Don't think so because even I don't know or met them before. Then how did you get to know about their profession when you don't even know them? Obviously, the tools they use tell about their profession. For any profession, the first requirement is having proper set of tools to work. That means even programmers need tools. First, they need computers and necessary hardwares, but very important tool in the programming is installing the platform for writing the code. Think you have understood already to learn and use Python or say any programming language, it is important to install the platform to write and execute the code. For Python, you have a lot of options to choose from. Actually, that is the real problem. With the more option and freedom comes the more confusion. Which one to choose? You can use editor or developing environments like VS code, Pycharm or Spider for Python programming. Can even use Jupiter Notebook, which is open source web based application runs on browser. All these platform offer free version. How sweet. This is the best word one could hear in this world. You can use multiple platforms if your hardware allows you to do so. If you're using Python for data science projects or for scientific computing, it is highly recommended to use anaconda. Don't go to Amazon searching it. I don't mean that big snake, but popular Python and R distribution. Anaconda has important packages pre installed in it, and installing any new packages is also a bit easy. You can use the different environments and choose whichever is comfortable for you. Now I'm taking Spider, for example. Don't worry, I'm not talking about the insect. I don't know why Python is so wild that it is mostly associated with the names of animals, Python, Anaconda, Spider. I don't think these animals use Python regularly. If you know, then please let me know. Okay. Look at the interface. Here is how it looks. Part where we write the program is editor. You can interact and get the output printed in the part called console. I will write simple lines of code. Don't get afraid about the program. It is just for demonstration. I'm just printing the version of Python I'm using. Save the script you write locally. Now it is the time to execute the program. To run the program, click on the run menu or alternatively, click on this sleeping triangle shortcut. You will see the output in the console. Almost all editors have similar interface. In this training session, we use Jupiter notebook as interacting is easy and dynamic. The interface of Jupiter notebook will look like this. In the Jupiter notebook, rectangle you see here is the part where we write the program, which is called code cell. To run the program in code cell, click on this square. Shortcut to run the program is Shift plus Enter. The result you are getting is the output of this particular cell. You can write the next code snippet in the next cell. Jupiter notebook has that simple interface. To better understand and get the hang of the interface, you need to go to the interface and try to work on yourself. You will understand better. I think this introduction about the interface will be enough to get started. Other things you are supposed to know about the interface, you will explore on your own when you practice. Now comes the interesting part. From the next video, let us start writing the programs, see you in the next class. 4. print() function: With all that good introduction, it is good time to start writing the simple programs. You tell me now, which is the simplest program one can start with. Before going through that, first answer this question. What is the basic task young kid or even parrot can do? The simplest task that a kid or a parrot can do is repeat what others say. That is the easiest thing one can do in this world. That answers our original question too. Most basic task Python could do is print the input statement as it is like parrot repeating the words. To make it clear, printing the message like hello world is the most favorite program of every beginner in any language. It is the time to introduce the first friend of coding, the parrot of Python, the print statement. Syntax is write print, open parenthesis and include your message or statement within single or double code. That's it. Now let's run the program. Congratulations. You wrote the first program. Try yourself with any message like hello world, but strictly use single or double codes. Otherwise, you get error. Python won't bother what you have written inside the print statement. It prints whatever you ask for. Now you know Python print the text within codes, but there is a problem. Sometimes we may need to include single or double codes within the statement, like highlighting a word or apostrophe, like in this example, but using the code within the input statement will confuse the Python. Such usage make it difficult for Python to understand which is the start and end of the input statement inside print and totally disturbed input statement. Python says, Hey, man, I don't understand what you want to do in its own language by giving error. If you're supposed to handle such situation, we must explain to Python in the language it understands. Here comes our new friend backslash for help. Whenever codes need to be used within the text, use backslash before the code. This tells the Python that we need to include the code for the printing statement. Python understands what it is supposed to do. You get the required output without any problem. Backslash help you to solve one problem. Before you thanking backslash, you need to know more about backslash. Backslash help us in multiple ways while programming. To be more precise, backslash is used to give special message for the Python. Let us explore a few of them. One such usage, backslash N gives the message to the Python to end the current line and start a new line. So do you love to use Imoges in your program? You got covered by backslash. You can print the faces also using the backslash, but you need to remember the unique codes of each of the faces. We don't use Imoges usually, so we don't dive deep into it. I hope you have understood how to use print statement. Print is one of the predefined functions in Python. There are many such predefined functions like print in Python that you will see throughout this learning. Print has easy syntax, but some function may not be as easy as print. When you have doubt on how to use any function, you can get help from Python directly. After learning only one function, you are too early to get doubt on how to use it. I know you are very capacitive, but in case while working with the Python predefined functions, if you're struck with the question, how to use the function, get the help directly from Python. Who will know about Python better than Python itself. For that, just type help and include the function within the parenthesis. Pan gives the information about the function like what it does and how to use it. Help will help you on your way and one more thing to remember. Be ready to be comfortable with the errors. You will regularly face a lot of errors while programming. Most of the time, errors are self explanatory like this error, zero division error, division by zero. If you know mathematics, then you understand that integer cannot be divisible by zero. In case, if you get error in the program that you do not understand, simply ask your most knowledge teacher ever in the history, the Google by searching the error name, you likely get the answer. As discussed earlier, the big Python community help us in resolving the error in different forums. Python is cool, Printing any message will take just one line of code in Python. The simple syntax of Python reduces a lot of effort that are required for other languages. We have just kept one step ahead. We shall explore more interesting syntax in upcoming videos. 5. Python Datatypes: Welcome to new model on data types. Before understanding the concepts, let me ask you a simple question. Can you build any product without using raw material? Silly looking question as answer is obvious. Building physical product is not at all possible. But someone might be thinking smartly that it is possible in case of digital products that are built using software, then you are wrong again. Even the softwares or programs need the raw material, but this raw material will be different. Physical product need physical raw material, but for programs, material is not in physical form, but is in the form of input data and instruction of what to do with that data. Data and instructions are the raw material of a program. So for any program, data is a necessary part. In this module, we shall understand about the data in more details. We first get to know about our neighbors before making them friends. Similarly, getting to know about data is very important step before start using the data. Just like there are many categories of people we see in this world. There are many types of data and we need to handle them differently. For example, companies collect the feedback from the customers in the form of text data. They process and publish financial details in the form of numeric data. Some data might be in the form of images, some in the form of video like this course. We gossip in the form of audio and there are many other data types. Just like we deal differently with different types of people, it is important to know the type of the data before we work with them. It is the time to explore the types of data commonly used. Python data has six popular children. All children are different from each other. They are numeric sequence, mapping, set, Boolean, and binary. Now make some time. We shall attend the data types party and shall meet each of its children, know them better and know about their children too. 6. Categories of Python Data: Welcome to Data types party. We are here now to meet each of the family members of data types one by one. We shall first meet the sequence type. The term sequence in English indicates the series of related things or events. You might have heard of sequel of a movie. The term, you might have understood sequence data never come alone because each member of sequence has their own gangs. That means sequence does not refer to single value, but to the collection or group of values. Sequence has three kids, string, list, and tuple. In this module, we meet only string because list and tuple are not just data, but the collection of data belonging to same or different data types. Hence, we will have a detailed meeting with them in the model Python data structures. Okay, let us start understanding string. String is best storyteller of Python or any language. I said that all members of sequence type have their own gangs. String has gang of characters. These set of characters form the word or sentence. In the simple term, it represents the text data. Text data is something you know in and out. All written contents in email that you have sent to your boss, SMS sent to your girlfriend, comments and feedback collected from the customers are among the examples of string. The text data you see here is a string. Earlier we saw the print with input statement. I hope you have not forgot it. That statement inside the print function is also a string. String is king of data types and hence require a special treatment to be included within single or double quote. That makes clear why we need to include the input statement inside codes for print statement. Because the statement we have provided is a string. When we use other data types in print statement, we do not use codes. We shall see later how print statement handle numeric and other data. Fine, I have got a piece of data here. How can I confirm the type of the data I'm using? Is there any function to know the data type? If you want to know what is the type of the data, just type type, confused. Yes, it might be, because we have used a sequence of types in our sentence. I will make it simple. I mean, use type function with the data within. Type is asking the piece of data to introduce itself. It replies that I'm string in this case. We shall learn about string with much more details later. This is just introduction class and we shall meet the other two gangsters list and tuples later. As they are gangsters, you cannot meet them easily. Just kidding, even they are very sweet. Both list and tuples are collection of data belong to same or different data types. We shall understand other data types and their applications first, and then we can proceed. Moreover, both of them have gang of elements. Only difference you may spot is list is included in brackets and tuple has parenthesis, but there is much more difference among them. Hence they feel similar and may confuse you. We learn about them detail later. The next child of Python data, numeric. Its name speaks a lot. It is not the cool data type for those who are allergic to mathematics. Numeric family is a math love because they all are good at mathematics. It has, again, three children, integer, float and complex number. Want to meet these kids? Why not? We came here to meet the whole family of data types, so we shall meet these kids too. Eat first child integer. Integer represents literally any real number without the tile of decimal part. It never deals with fractions. Integer can be a whole number, including zero and negative number. All value you see in the cell are integer data. Integer is okay with anything, say positive number, negative number, or even zero, but it hits the decimal part. If there is decimal part to the number, then integer will become angry, kicks them off from their territory and abandon data gets into the next category that is float. Float is short name of floating point numbers. Floats are real numbers with decimal part. Adding just 0.0 to an integer will not change the value of the number, but change the data type from integer to float. The programs involving heavy numerical calculations usually get flooded with floating numbers than integers, and it is more practical. Look at this simple example. Dividing an integer with another integer can make the resulting value a float. Hence, I told float is more practical. Apple with orange cover over it doesn't make the apple an orange, but numerical data within single or double coat represents string data. Never use coat with a numerical data. Not just numerical data. Do not use it with any data other than string. Another numeric data type is complex number, which is complex as its name suggests. It has complex part root minus one. In mathematics, complex number is represented by I, but we are bit different. In Python, complex part is represented by J. This change is because Python love electrical engineering more than others, and in electrical, I represents current and J represents complex number. Remember this while using the complex number. The next family we meet is map. The mapping is the type of the data where the information is stored in the form of key and value pair. Key is the clue for the data stored in the form of value. If you could crack the key like Sherlock home finding the clue, then finding the value is KK. Now come to the next datatype that is set. Like list, set also roam around with its team, but each member of the set is unique. That means there is zero tolerance for duplicate entries. The team hides inside curly braces. There is also logical datatype in Python that is Boolean. Booleans are like young kids who always tell the truth, but do not give any other information than true or false. They can speak only these two words. Even though it talks less, it is very important data type to check conditions that we see in details later. Boolean values are case sensitive with the first letter in upper case and rest in lower case. Otherwise, Python do not treat it as boolean. Don't put the boolean values in codes. Otherwise, they will be considered as string. And finally, binary is the secret agent of Python data types. It uses the secret language to communicate, which is in the form of zero and one. This is the language with which computers talk with each other, store all the values in its memory. Use zero B in the beginning to tell the Python that this value is a binary. Otherwise, Python will think the value is an integer, as it is the language of computers that we do not understand. We do not talk much about it. I hope you have enjoyed the party of Data Types family. All members of family are unique and has their own significance. I know you could not communicate in detail with some of them, but don't worry. By the end of this course, you get the chance to talk with them. See you in the next class. 7. Datatype Conversion: And I assume you have many friends and relatives. You have got friends from school, university, work, and might be some from social media and friend like me from this course. But how many of your friends are your best friends? Hard truth of the life. I'm sure very few of them. Is there any reason we like some people more over others? There could be many reasons, but very commonly, we love to connect with people having something common among us, like same school, profession, similar likings, to name few. But why we are discussing psychology in Python class, there is a reason even data belonging to same data types like each other and they can be operated with each other effortlessly, like adding two integers, float or string. But data belonging to different data type can also be operated with each other. For example, we have two numbers. One is integer and one is float. Both belong to numerical category. You can add them and the resultant number has a decimal part. Hence, it is a floating point number. Here, Python first converts integer into a float and then add it to another float. Python do it by itself without asking your permission to do it. This type of conversion done by the Python without the help of the programmers are called implicit conversion. But there are some cases that arise while programming where we need to convert the data types manually using functions. Here are a few examples to understand how it is done. In first case, input data is a numerical data enclosed within codes. By default, Python treated as a string, but it is an integer from its heart, we shall bring it to its actual type. We manually convert the data into integer using function. In this case, again, the data is numeric, but according to Python, it is string. Using the float function, string is converted into float. Next example, data is an integer. We use STR function to convert the integer into string. And the last example, data is float. Using the int function, we cut the decimal part of the float and convert the float into an integer. These are the few examples of converting the data types. These int, float and STR function doesn't care about the datatype of the given data, but try to convert them into integer, floating point and string data type respectively, if possible. You can try a few other examples like integer get converted to float. This type of manual conversion of data type where you, the programmer, request or order the Python to change the datatype is called explicit Conversion. I know you ask about the application of these concepts. Let us go step by step. We shall see their application when we proceed with the programming. As of now, I'm feeling hungry. I will convert the batter into bread using explicit conversion. 8. Introduction to Operators: In this module, we shall go back to our initial school days. We all started learning mathematics in school with numbers or anyone else here who started with calculus or trigonometry. I hope everyone started with numbers and counting. But knowing just numbers is of no use as solving any numerical problems need the operators. Actual learning of mathematics has started with the operators like addition and subtraction. Computing without operators is same as lock without key. It is just useless. Hence, operators are the key requirements of problem solving. Same or similar operators, we use in Python for problem solving. There are three categories of operators we use in programming, arithmetic operators, comparison operators, and logical operators. Remember, operators are the spices of programming. They just give more flavor and fun to the boring codes. No concepts we learn in this module is new for you. Most of the concepts are same you have learned in your schools. Hence, this module will bring back your school memories. Are you ready to time travel back into your childhood? Let us go back to our primary school to brush up the concepts of operators one by one. 9. Arithmatic Operators: What is the key requirement of any numerical calculation? Don't tell me you need a calculator. I know you're very smart. Even calculator cannot calculate without the arithmetic operators. Let us start with the basic arithmetic calculations that we have done in schools, like addition, subtraction, multiplication, and division. What else can be easier than this? Let's start. Addition is an adhesive which bring the best friends together forever. You know, you can add numeric data. I assume your teacher taught addition well so I don't go deep. But one thing, first two lines have numeric values. First line has two integers and second has two floats, which are added. Never use code for numeric or any value other than string. Addition of these values are performed and results are printed in the order. Can observe here, we can even add two strings. Adding two strings will concatenate them end to end. That means second string is joined at the end of first string. That's all about addition. Subtraction is a magical stick, pulling out the two slices of pizza from four and make it disappear, leaving behind 02. I don't want to be your early school math teacher. You know it already, and let's move on. Multiplication is a photocopy machine that produce duplicate copies. It is taking five documents and making six copies each, producing 30 copies total. Division is nice and honest friend who divide the treat equally. In programming, asterisk is used for multiplication and slash for division. Multiplying a string with an integer result in repeating the characters of the string that number of times. But you cannot use division and subtraction on strings. These operators are simple, want to learn new operators. There is a special division called flow division, which use double slash to return on the integer part of the output. This is useful in situations like dividing the people among teams. For example, in this case, seven people need to be distributed among four teams and how many people each team can accommodate if strength of all teams must be the same. If you use division, it says 1.75. How can we cut the person? Number of people in each team cannot be decimal if they're alive. Floor division return the integer value after division. Each team can accommodate only one person what to do with the rest three people? Let us come back to it soon. Another popular operator is exponential. Exponential make the things super big. Double asterisk does this task. Here, two is rises to the power of three, which is eight. This magical operator make the two into eight. The same operator could be used for the roots, for example. Power of one by two represents the square root and power of one by three for cube roots and so on. Nine raise it to the power of half is square root of nine, which is three. 64 rise it one by three is cube root of 64. The value has a lot of decimal, still this value is four, as you can observe. We shall see rounding the values later. Look at one more operation, modulo, which use percent sign. Don't think it returns the percentage of two numbers. It returns the reminder when first number is divided by second. Want to understand more. It is very simple. To understand this, recall floor division. In floor division, we distribute the people equally among the team, and leftover people make their own team of reminder. We have seven people to divide among four teams. We have provided one each leaving behind three people. These three make their own team which is strongest than the other teams. If we can divide all people among the teams, like in this case, where nine people need to be divided into three teams, which can equally accommodate three each person, then obviously the remainder is zero. After distributing equally, no person is left out. You got to know the arithmetic operators. When we use operators in combination, use parenthesis for prioritizing the operators. You can look at the order of priority in this table. Python follows this order for operations. The calculation within the parenthesis is carried with priority. Operations in the innermost parenthesis, which has highest security from the parenthesis is carried first. Two plus three and three plus four is processed first. Then both value after addition, five and seven are individually rises to the power of two. This is because exponential has more priority than addition. Five squared is 25 and seven squared is 49. Then finally, both are added to get 74. This is what we have done in cube root of 64. 1/3 operation is protected within the parenthesis. Hence, it is carried out first, then the resulting value is used for exponential. You have the control of priority just by using the parenthesis. If you need more time to watch and read the table, then I will give permission to pause the video. I am sure arithmetic operators are super easy and comparison operator, which we see in next module is also very easy concept. We shall meet there. 10. Comparison Operators: Do you know what is the one big bad habit of humans? I know we are loaded with bad habits, but your task is to find one bad habit that kept us away from the happiness. Guess, we humans always love to compare. If you are not guessed it correct, don't worry. It will not be asked in any exams. Always judged by comparing with others, maybe in terms of beauty, education, career, salary, and whatnot. Comparison might be the major reason for unhappiness for us. But in programming, comparison is an important parameter in making decisions. For example, if you're working in company A and you are offered job by company B, how will you make the decision Silly by making the comparison of different parameters? First thing we look at is salary, who don't like money? If salary offered by company B is higher than your current salary, then switch, otherwise, stay back and try your luck. I can hear someone saying you don't make the decision just based on the salary. I need to compare many other parameters like project role, work environment, work life balance, what your neighbors think about both companies and many more. Again, all these parameters need comparison. In mathematical term, we use comparison operator for this purpose. Which are those operators we use for comparing? I'm sure you know these two. Here are the list of comparison operators used in Python and result of these operators are Boolean data type that is either true or false. If the provided condition is satisfied, it return true, and if the condition is not satisfied, it returns false. Let us understand them one by one. Greater than is the judge of talent show, which always look for the highest scorer. If the value on the left hand side is greater than the value on the right hand side, greater than return true, if not false, here seven, which is on the left hand side, is greater than five. Hence it return true. If the values are equal, like in this case, where both left hand side and right hand side has five, the outcome will be false. Because as its name suggests, it strictly look for greater than. For the special purpose, we have greater than or equal to. Greater than or equal to is the fellow judge for greater than who is a bit liberal and consider the one who has similar score two and pass them. It return true when the value on the left hand side is greater than or even equal to the value on the right hand side, so it is a bit liberal than greater than. If you understand this well, then we will have just opposite of it. Lesser than and lesser than or equal to are the judges of race computation who check for the least time to achieve the target. You tell me now the outcome of this condition is five less than or equal to three. Five is neither less than three nor equal to three. So you get false. The next operator is equal to. Equal to look for perfect match like matrimony site which look for the interest matching. If both values are same, it return true, otherwise, false. Use double equal symbol for checking equality as single use indicate assigning the value to variables. Another scary looking term, variable. We have a separate module on that. Coming back, this time, let us use string. String ABC is checked with ABC. They are equal, so true is 5.0 001 equal to 5.0. Comparison operator are very strict. Even if the values are very near, it return files. There is an opposite to equal to that is obviously not equal. Adding exclamatory sine before equals indicate if the condition is not equal to. This is a weird operator who do not like the identical twins. This operator returns false when both values on left hand side and right hand side are same. In any other case, it returns true. Phi is not equal to three, hence it is true. Hope none of these operators are new for you, but the operators used might be new, but still they are easy. Here we see a few of the tests of comparison. If you have understood the concept of comparison, this test doesn't need any explanation. Still, I will make some time for you to take around. In the first case, programmer asked the Python, Hey Python is three less than two, three is definitely not less than two. Do you expect the output to be? Whatever your expectation might be, but Python says no, by returning the output false. The next case is three less than or equal to three. Three is definitely not less than three to best of my knowledge, but it is equal to three. Hence output is true. If there was less than operator here instead of less than or equal to, then story would be different. Nothing serious will happen, but you would have got false. That's it. Is three greater than two. Yes, it is two greater than or equal to three. If three is not less than two, then how would two is greater than three? This game is not so interesting as you know the result of these. So I will stop here. You can look at other operations. Easy, right? And don't think two and three are my lucky numbers. I'm just a bit lazy to find other numbers. Before we end the lesson, can we compare two values belonging to different data types? At this example. In the first line, a float is compared with the integer. It is totally fine to compare them because they both belong to numerical data types, but it is not okay to compare the values with strangers like string in second line. Comparison is okay, but in programming, there are few use cases where we need to combine two or more conditions. It helps us to compare multiple condition before we arrive at the decision. We connect two or more conditions using logical operators which we see in the next class. 11. Logical Operators: This word is very peculiar. We cannot make decisions just by considering one condition. We need multiple conditions in the favor for higher probability of success. Forget that difficult philosophical sentence. In simple words, what I mean to say is we cannot make decision just based on comparison of one parameter. In the previous lesson, we have tested multiple comparison conditions individually. Some case, we use multiple comparative statement before coming to a decision and these conditions are combined by a class of operators called logical operators. Even logical operator is something you know already and use them regularly. There are three logical operators commonly used. They are and and not familiar words. We use them regularly in English. Their logic as a logical operator is also similar to that of English. Let us see them as logical operator one by one. First, let us start with and. Imagine you go to restaurant, you order pizza and sauce. We use and in between pizza and sauce because there should not be option of having any one. You strictly need both to be delicious. How can I just eat sauce without pizza or other way around? Can I say it in programming term as both conditions need to be true for getting the conclusion to be true? This is an example of two conditions and there could be use cases of more conditions to be satisfied. Logic behind and is all conditions need to be true for the conclusion of the statement to be true. And is a strict professor who does not like to compromise in any situation. It expects every condition to be perfect true for the conclusion to be true. In other words, result of and is true only when all conditions are true. Otherwise, it's false. For example, is six greater than five. Yes, it is true. I six less than ten unless you are a preschool kid, you know very well that both these conditions are true. So both conditions are true and hence resulting and condition is true. Take the example of multiple conditions. Here, all conditions are true. Hence the result is true. Nine conditions true with just one condition false, make the whole statement false. I hope now you perfectly understood and condition. Now let us move to next operator, how you use R in your routine. When you go out with your friends, you like to have pizza or burger, whichever is available. What this R is saying, you need any one of them to get your stomach full. If luck is in your favor, you get both, which will make you fully satisfied. I interpret this as even any one of multiple conditions in R is satisfied or found to be true, the whole statement will be true, right? Our statement is very optimistic. Or statement will be false only when all conditions in the statement are false. Otherwise, it will return true. Unlike condition, even if one among ten conditions are true, then output is true. There is one more logical operator, not get back to the old story of restaurant with your friends. Imagine restaurant has only two options to eat pizza and burger, but you do not like pizza, so your order condition is not pizza. By using the logic knot, you mean you are okay with anything except pizza. So you are left with no other option than eating burger. Same logic do not operator carry in programming. In conditionals, you have two options, true and false. If not true, then it must be false. In some way, it is like your spouse. If you are true, it is false. If you say false, it will become true. Is one greater than ten. No, it is false. Not operator which heads whatever comparison operators say and does the opposite, say this condition is true. I hope you have digested naught operator to. Comparison statement and logical operators are very useful in conditional if statement and in loops like four and Y loop. We shall discuss about them in later part. Here is one simple example of using logical operator, but why English alphabet appeared suddenly. But this code is still easy to understand. A is the name given to the value six and then we use its name instead of value. A modulo two, that is six modulo two is zero as six is divisible by two. Six is less than ten, also six is greater than zero. All three conditions are satisfied in this statement, so result is true. Similarly is this example. Here, value is the name given to the value 13. The value 13 satisfy only one among three conditions. That is value is greater than zero. Only that condition is true. Both others are telling lie. But these conditions are joined by operator, which has kind big heart enough to excuse two falls among three. R operator will be happy even when only one among multiple comparisons are true. That is the optimistic nature of operator. Hence, I told operator has kind big heart. In these two examples, values are given with distinct names. This naming ceremony is called assigning variable. This is the ingredient of next module. I'm inviting you to the naming ceremony which occur in the next module. 12. Variables & Identifiers: And Welcome to the land of variables and identifiers. Think about it. Just as each of us has a unique name, so do the piece of data we work with in the programming. Name give us identity, recognition, and a touch of personality. So why shouldn't data get the same treatment? Imagine calling everyone, Hey, you, it would be chaos. Data deserves the same respect. So in programming, we name our data for easy identification. Under variables, our data's very own name tags, variables are the data name tags. When we are working with the data in Python, we assign each piece of information a name like sticking a name tag on it. This name is called a variable. Think of it as the naming ceremony for the data. Just like giving a pet a name, you are giving your data a way to be recognized. For example, if you assign a value to a random variable A, then anywhere you say A in your code, Python knows you're talking about that specific value. Here A is a variable. It is like saying A is 13. From now on, you can use A in your code and Python will understand that you mean 13. If you ask to print A, it print 13. Now there is another term that often shows up and sometimes sounds a bit scarier identifier. Before we move ahead with the variables, let us understand identifiers. The fancy term for names. Don't worry. It is simpler than it sounds. An identifier is basically any name you give in the programs. It could be a variable, a function, or even a class. You might not aware of all these terms, but you will learn them. For now, think of identifiers as a big umbrella term covering all the different names you will create in your code. To sum up, remember, a variable is an identifier for a specific value like age or height. An identifier can be a name for almost anything in your code, variables, functions, classes, and more. Big umbrella term covering names for all kinds of things. In simple term, all variables are identifiers, but not all identifiers are variables. Picture it like this. If identifiers are a big VIP club, variables would be one of the cool members. Are other members too, like functions and classes, but variables are the ones that we often start with. I hope it is clear for you. In short, naming data isn't just about organization, it is about respect, readability, and future proofing your code. Next time you assign a name to a value, remember that you are giving your data a little identity and make it easier for everyone to understand. When you assign a value to a variable, let us say product sold is equal to ten. It is as if you have created a synonym for that value. Instead of remembering the value ten, you just remember the term products sold and whenever you need to update it, you just change the value without much worry. Now I assign products sold is equal to 20. Assigning the same variable to different value kicks out the previous value and save the last assigned value. Variables don't just make your code readable. They will make it editable, manageable and way easier to update. Previously A is assigned with the value 13. Now I assign five. Now value 13 is deleted for A forever. Use different variables for different values. Variable A is synonym with the value five. Any operations made on variable A is operated on the value five. That means A plus one is five plus one, which returns six and A multiplied with three is five multiplied with three, that is 15. This bond between A and five will continue till value inside A is changed. Here is another example where naming ceremony in action. Price is equal to 10.99 units. Discount is equal to two units. Final price is equal to price minus discount. Print final price. You asked the Python to print the final price only hence it returns the value of final price. Now you are not just working with nameless numbers. You have got price discount and final price. They tell you exactly what is happening and if prices change, you only have to tweak it in one place. But why variables are so handy? Imagine this situation. Consider a plot of rectangular shape with length 30 units and breadth 20 units. You need to find the area to provide the surface and the perimeter to put the compound wall around them. So you know mathematics well, you calculate mathematically, area is ten times breadth and perimeter is equal to two times length plus breadth. You understood what I have done here because you attend this session. But for the other person who is using the same program, but did not see this video session, cannot say if the program calculates area or the total price of 30 pizzas at 20 bucks each. This is an easy example. What if the program is bit complex like scientific and engineering problems, then you need to be ready to get disturbed as each person who use it need to call you to understand what this program does. Also consider the case, you need to save and reuse the value you get as the output. Like you got the local price of the land per unit area, you need to evaluate the price of the plot by multiplying the local price per unit area to your output area. You cannot do so as the value of the output is not saved. To do so, you need to write the values manually for calculations. What if there are several values need to be used in calculation? So let us make some changes to this program. I will create two variables, length and breadth. If you like short and sweet, you can call LNB, but I am not responsible if you confuse them later for lemonade and beer. Now calculate area and perimeter and we'll assign them to respective identifiers. Now I will print with a statement the area of the plot is and add respective value to it and similarly the perimeter. What is happening here? It is simple string addition that is concatenating the text at the end. But is this correct? No, Python has some problem with this program. The area and perimeter we have calculated are integers, or depending on the input values, they can be float ora a numeric value. The problem is the integers and floats are not relatives of string, and hence string is not ready to welcome the integer in their team. Now it is the best time to use the explicit conversion that we have learned already. First, convert the integer to string, and now string is very happy to accept the value. Now the program looks clean and most probably anyone with above average grasping power can understand what this program is doing. If you want, you can use the value inside the area and perimeter to any other calculations too. Great. Take one step ahead. Let us make the program more dynamic. Ask the user to define the values of length and breadth. That would be more practical. The programmer usually do not use the program, but develop them for the different user. Use input function along with some optional message for the user to understand enter the length of the plot and similarly breadth. Now again comes the problem of data types. Python consider all the user input data as string by default. Looks like Python love string more compared to other data types. What we shall do is convert them into integer data type. If there are decimal parts, then make it float data type. Now program asks the user to input the value of length and breadth and the value entered is assigned to the respective variables. User need to press Enter with each entry. Programmer don't have the headache of defining the values. What an easy concept. This is one way of printing output statements. There are other ways too. You can use this format instead. Curly braces used inside the statement represents variables and you need to define which variable inside format in the order separated by comma. First curbras represents area and second perimeter as defined in the format. Inside the format, each value must be clearly defined in the order for a change, make the input into float. Now execute the program and enter the value with decimal part. Looks good. If you do not want the long tail like monkeys for these values, you can limit the decimal by specifying the number of digits. Inside curly brace add colon dot, which means after decimal point, F indicate limit the decimal number of float to two. Now Python understand it need to limit the number of decimal values to two. The output is rounded to two decimal points. This is not the end. There is one more way to print the output. This method may be close friend for those who use C, C plus plus or Java. Here F represents float. There is different alphabets representing different data types, but do not use this method much in Python, so I will not go in details. Assigning value to identifiers make the program more effective and useful. You are giving the identity to the data or a function or a class. But with the power comes the responsibility. Python has certain conditions to select the identifiers. In the upcoming class, let us see the rules of selecting the identifiers, meet you in the next class. 13. Rules to select identifiers: Now, it is understood that variables or identifiers are user defined names. I know when you are provided with the authority to give the name, your creative self can come out with the identifiers like these. Can you provide such identifier? Do you have all the freedom to assign any name to the variables? Before understanding the variables, let us analyze our names. We get better idea. Do our names are randomly selected? I don't think so. We follow some protocol to select our names. Do your name has special character like Ampersand or dollar? Most likely no. Usually, our names don't have special characters and do not start with numbers, but sometimes may have the numbers at the end like few kings and emperors. Now let us come back to the main topic of rules to select the identifiers. When we follow some protocols for our names, then why not for the variables? If you are thinking you can assign any random names to the variables, then I need to disappoint you. But rules are very simple and don't have much restrictions. Here are the set of rules for selecting the identifiers. Rule number one, do you have any pet in your home? If not, then assume you have one as you don't need to pay anything for imagination. Also, imagine it has got same name as yours. I don't think anybody does it. But why? If your pet has same name as you, then what will happen? Nothing serious will happen, but the result is confusion. You will become confused if you are called or your pet. Same happens with Python. The first rule of selecting the identifiers is don't use Python predefined function and keywords as identifiers. Here are the list of Python keywords. Similarly, you have learned few built in functions like print input type, into float, and many more. Don't keep any of these names to your variables, otherwise, Python will confuse. Rule number two, as I told in the beginning, our names do not have special characters. Similarly, for identifiers, only special character allowed is underscore. If you're allowed to use special characters, then use it in your passwords. It will become strong. Python allow only letters, numbers, and underscore. Even space is not allowed. Use only underscore, if at all you want to use any special characters in identifiers. Rule number three, numbers are permitted to be part of identifier doesn't mean it has freedom to sit anywhere. No much restrictions, but first character of the variable name cannot be a number. Like front seats are reserved for VIPs, first character is reserved for letters and underscore. Numbers can be used anywhere else. There is no restriction for letters and underscore position. Rule number four, identifiers take upper case and lower case very seriously. Identifiers are case sensitive. Once you assign the variable name, be specific of the case of identifiers when you use them again. Both these variables are considered as different variables because of change in case, and that's it. These are the four conditions of variables. Here is the list of some valid identifiers. These identifiers do not violate the rules of identifiers hence they are valid. I know we learn what not to do better than what to do. So for better understanding, we should go through the invalid identifiers and why they are invalid. The first line contains two identifiers. As per rule number three, identifiers cannot start with the numbers. The second line, print input, format, help, map type are examples of Python built in functions. Similarly, the third line contains built in keywords. Stated in rule number one, predefined functions and keywords cannot be used as identifiers, so they become invalid. Examples in fourth and fifth line contain space and special characters which are restricted as per rule number two. With these examples, you have understood what not to do, which in turn help you to learn what to do automatically. Python is very user friendly and do not have much restrictions. Just follow these rules for identifiers. Python will be happy and will not bother you. But follow a few more rules that we explain in the next video to make your program cleaner and more readable. See you there. 14. Good practices of Programming: And Welcome back. In the last session, we covered the ironclad rules of choosing identifiers. Today we are exploring the friendlier, the good to have guidelines. The rules we have learned in the previous session are mandatory like wearing some cloth to job interview, and the guidelines we are learning, think of these as style tips for your code, like wearing a tie or decent grooming. Sure, these tips aren't mandatory, but they will make your code look so much better and you will thank yourself later. Following these guidelines will help you write code that even a stranger or future you, who is basically a stranger by then can understand. Imagine your code as a friendly conversation rather than an ancient text that need explanation. Are you ready? Here is how to make your code clear, approachable, and even a little charming. Good practice number one, let your code explain itself, name your variables like you mean it. Let us be real. We have all had those. What did I write here moments when we look back at our code. Especially if you have used mystery names for your variables like X and Y or A and B. Sure they are short, but they don't tell us anything about what they represent. Remember, the goal of code is to be readable like a friendly instruction manual. Let us go with a scenario. In the previous session, we were calculating the area of rectangle. You could go with that again. How does it look or the alternative, where we use alpha bets and short names like this. Both work for sure, but only one is easy to read and understand without scratching your head. The self explanatory version instantly tells you what each part of the code does, make it as readable as a friendly reminder note. Then what about mystery novel code? Well, even Sherlock home might struggle to remember what L, B and A stands for after a few days. Give your variable names that tell the whole story. Pick names like length and breadth over L and B. This is your future self thanking you. Your code becomes so much easier to read and anyone including you can dive in, understand, and update it easily. Good practice number two, use comments, give your code some friendly commentary. We all love comments on social media like reactions or compliments, but comments in code serves a different purpose. They are there to help explain the thought process, the calculations, or any tricky parts in your code. Think of commands as little signpost. They help others navigate your code, trust me, they will help you to a month later. In Python, commands start with the pound symbol. Anything that follows pound on a line is ignored by the Python interpreter like it is invisible. Feel free to use commands to jot down explanations, hints or warnings. Now, don't get carried away and start leaving a comment for every line. Imagine reading a book with a footnote after every sentence exhausting. Instead, place comments strategically to clarify complex parts, for instance, like this. And if you ever want to ignore a big section of code, maybe because you're still testing it or haven't quite perfected it yet. You can use triple codes. Don't search your keyboard for triple code. Use single code three times. Triple codes ignore everything within them, making it perfect for putting code on pause temporarily. By thoughtfully placing comments, you give your code a built in guidebook. It becomes understandable, maintainable, and approachable so that different people or future you can easily pick it up and work with it. Good practice number three, keep things organized. Clutter free code is happy code. Just as TD desk is easier to work at, organized code is easier to read and debug. Keep related pieces of code together. Use blank lines to separate logical sections and avoid cramming too many tasks into one line. You don't need to pay anything for leaving blank line, but don't leave several lines blank, making the programmer search where the next line is. Clear structure keeps your program from looking like a wall of words. These practices aren't strict rules, but they are golden advice for writing cleaner, friendlier code. When your code follows these principles, anyone, including you can jump in, understand what is going on, and feel confident making changes without breaking something unintentionally. Think of these tips as your code user manual. So keep these good practices close. Practice the concepts and rest up. There is more code to write, and this is just the beginning. Until next time, keep it neat, keep it readable, and keep it fun. 15. Understanding String: Welcome to the fascinating world of strings. If you have ever sent a text, drafted an email or left a low note, you're already a pro at using strings. You just didn't know it. Strings are so much more than just random text in programming. They are the lifeblood of communication, the rock stars of data types, and the reason why every programmer double checks their email before hitting send. I mean, who hasn't feared sending an awkward typo to their boss or even worse a message with that typo to their crush. In the world of code, strings are the superstars that wear the crown of single or double codes. Think of it as the crown jewel of the programming world. Without it, string lose their royal status and can cause chaos. Forget those codes and the program things you're talking about a variable. So strings always wear their crown with pride, whether it's single coat or double coats, because let's face it, they need that royal flair. But why are strings so important? Well, think about it. Every time you visit a website, order food online or leave a review, you're working with strings. Text is everywhere, and programming needs strings to manage all that text. Applications, websites, games, almost every program has strings working hard behind the scenes to make sure things look right and sound right. Even when you input numbers, your program sees it as text until you tell it otherwise. In the kingdom of code, string data is the default royalty. If you are ready, let us dive deep and dissect the anatomy of a string. We are going to break down what makes strings. Who knew text could be this thrilling prepared to witness the secrets, the powers, and yes, even the occasional drama that comes with understanding strings in programming. Just like each of us is known for our unique set of characteristics. Strings in Python have their own identity and it's all in their characters. Yes, a string is simply a sequence of characters, each one holding a place in line to create something meaningful. You can think of characters as the building blocks of a string. Every single one counts. Even though sneaky spaces, we are creating a string, which contains, this is a string and assign this string to the variable named statement. Want to know the length of a string, Enter Python's magic word, Alan, which is length function, feed a string into the Alien function and it will count every single character and give you the total. If you try for this particular string, you will get 16 because Python dutifully counted each letter, space, and punctuation mark if it was there. Don't search it here, we don't have it. 16 characters, each one essential to make this string meaningful. Let us talk about index, Python's unique counting style. Every character in a string has a specific spot, which we call an index. It is like each character is sitting in its own assigned seat and the index number tells you exactly where that seat is. But here is where Python gets quirky. Looks like Python had a bad math teacher. Python starts counting not from one like most humans would, but from zero. Yes in Python world, zero is the starting point. For any given string, first character has the index zero. The last character will always be at the index of length minus one. For this particular string, length is 16 and last character has the index 16 minus one, that is 15 simple blame it on Python's math teacher if you find it odd. Space matters every character's count. Don't underestimate those spaces. They are characters too. Python doesn't ignore them. They are part of the strings charm, so they each get their own index just like every other letter. For this string, there are three spaces which give the clear meaning to the string. Without these spaces, the string would be just sequence of characters without any meaning. Now let us talk about negative indexing, reading from the right. Here is where Python really mixes things up. Most of the world encourages you to be positive, Python is totally cool with negative indexing. Instead of always starting from the left, you can also count the characters from the end of the string, moving from right to left. Here is how it works. The last character has the index of minus one. The second to last character is minus two. It goes all the way back to the first character, which has the index of minus length. Whether you're counting from the start or the end, Python got you covered. Hold tight because we are about to explore the art of poking around inside strings. Curious about what is at the specific index, let's pull out our trustee magnifying class and dive into the magic of indexing. Imagine a string is like a row of lockers, each containing a character. Each locker has a number called index, starting from zero. You want to know what is hiding in locker zero, you just check string with the index in the square bracket. Here is how it looks in action. Index zero, you unlock the first locker and Python returns uppercase T. If you check Index 15, you scroll down to the last locker and it is holding a character G. Index minus one, wait, a backdoor to the last locker, indeed. Python says, Why stop at positive numbers? Let us count backward two. String with the index minus one also reveals the final G. But what if you are too greedy? Let us say you're feeling adventurous and try to open the locker 16 in a string that only has 16 characters from indexes zero to 15. Python is going to glare at you like a librarian when you talk too loudly. Here is what happens. You ask for index 16 and Python snaps back index out of range. Are trying to grab something that doesn't exist, calm down. Think of it like this. If your string is a party with 16 guest, having the index zero to 15, you can't expect Python to find a guest at seat 16. It is empty. No matter how hard you insist, Python will not pull the character out of thin air. You have understood the structure and index of the string. Let us learn in the next session to slice the strings into parts using the index. Take a small break and join fast. 16. String Slicing: Let us slice drink like it's pizza night. Slicing a word that instantly brings joy to pizza lovers and fruit fanatics alike. Whether it's cutting into the perfect cheesy slice or just snatching the part of the cake with the most frosting, we all love a good slice. And guess what? String feel the same way. They're now being sliced into smaller bite sized pieces. In programming, we call these tasty morsels from the string as substring. Slicing is the operation that is performed not just on the strings, but on all the sequence data types like List and tuple. The concepts, syntax, everything remains same. So learn string slicing. You get List and tuple slicing for free. Are you ready? Now imagine your string is a pizza. Instead of toppings, it is packed with letters. You are handed a knife. Don't worry. It is a friendly one, and you are ready to cut out the exact slice you want. Welcome to the string slicing in Python, the art of cutting and serving strings, one substring at a time. Let us get to slicing. Here is your delicious string pizza for the same string statement, which contains This is a string. Now let us use Python's slicing knife to get exactly the slice you crave. The syntax, it is simple and works like magic. String name along with start index, end index, and step size separated by colons inside square bracket. Let us break it down. Start index, where your slice starts. End index where your slice almost ends because Python is a Ts. It stops at one less than this index. Step size, how many steps you take between the characters. Want every second character, use two, want every third, use three. Skip none, leave it blank or use one. For example, the first slice, let us slice up. This is a string like this. Statement with one colon five colon two. Let us see start at index one. The character here is H at index five, but don't include it. So we stop at index four. Step size two, we skip every other character, so it consider the character at index one and three. Slicing is topped at index four, five is not included. Index one has H and Index three has es. Hence grabbing H and yes, one colon five colon two gives us the slice Hs if any of the arguments are not mentioned, then Python do not get Fright. It will assume the default values without your permission. For example, if index excluded, so if you ask for one colon five, you are really getting everything up to four from one. Think of it as ordering pizza from slice one to slice four. Default values are your friends. If you skip one of the parameters, Python steps in with some default values. Skip the start index, it start at zero. Skip the end index, it goes all the way to the end of the string. Skip the step size, I grabs every character that is step size is one. In first case, no argument is mentioned, so Python need to assume all the values by default. That is start index zero till the length of the string in the step size of one. But what is the use of this statement? It returns all characters as it is. Instead of this, you could just print a variable. This is like asking to slice the pizza and demanding all the slices. The second line, first two arguments, start index and end index are provided, which has two and eight respectively, and step size is skipped. So step size is assumed default, that is one. If step size is one, you can skip the third argument as it is default. No need to provide even colons for third part. In second case, we'll return the characters from index two till eight minus one, that is seven. So all characters in index 2-7 are returned. In this case, first argument, start index is not mentioned. Second argument, index is ten, and again, third argument is missing, so it will return index from start till one less than ten, that is nine. All characters in index zero to nine are returned. Getting something, take few more examples. What the code will do in this case, here both start index and end index are missing. Only step size is provided that is two. The program will return the characters from start to end in the step size of two. That is every alternative characters are returned. In the second line of this cell, slicing starts from index lend till end. I hope no need to mention that step size is two, shocked. Just checking if you're listening or just sleeping. No, step size is one. All right slicing wizards. Get ready. Let us go one step ahead slicing in reverse, and now it's time to master the backward slice. Think of it like rewinding your favorite song or moon walking through a string. The plot twist, start index is greater than the end index with negative step size. Here is the scene, starting at middle of the string. End index is two way to the left. Step size is minus one, time to move backward. What is going on? Negative step size flips the game. Normally slicing moves from start to end. But with minus one, we move in reverse from right to left. Python, it is clever enough to know what you want as long as you provide some instructions. So print statement with ten colon two colon minus one. How this works, start at index ten. This is the letter S move backward to index three. Index plus one, unlike minus one in positive steps, you grab every character until index three in the reverse order. Output looks like this. Notice how with a negative step size, the end index works differently. Python includes one more character beyond the specified end index. It is like giving you free extra slice of the cake. Do you think it is true? Think again. Let's take it up a notch. If the start index is missing and the step size is negative, Python thinks, you want me to slice from very last character back to your end index. I got it. Ask it to print statement colon colon minus one. This is what happens. Start at the end. Python assumes the last character, index 15, which is G. Move backward to index six, which is end index five plus one. Python slices everything in reverse until it gets into index six. Output looks like this. Isn't Python very clever? Now, the big finale, reversing the entire string. Here comes the ultimate trick. Want to flip your entire string backward, skip the start and end indices and go straight for step size. Print statement, colon, colon minus one. As step size is negative one, Python starts at the last character. Move all the way to the first character. Prints the string in reverse order as it is minus one. Output looks like this. It is like watching a movie backward, where a hero falls back into the burning building and unmeds the love of their life. The golden rule, step size cannot be zero. Now a quick word of caution. Your step size can be positive, negative, or missing, but it can't be zero. Why? Because Python isn't going to sit there staring at the string, wondering, should I move or not? Zero step slicing is like trying to walk forward while standing perfectly still. It is just not happening, so wrapping it all up. With slicing, you have unlocked the full anatomy of strings. You have mastered the art of controlling strings, moving forward, backward or skipping along as you please. So go ahead, slice and dice your string like a pro, and always remember Python has caught your back. Even when you're slicing in reverse. In the next video, we shall see a few methods operated on string. 17. Methods on String: Oh Welcome back. In this video, let us learn important methods operated on string. Shall we proceed? Let us turn on detective mode. Find the index of a character. Earlier, we found the character at a specific index like playing hide and seek. But what if the table turn? What if you are the seeker and need to find the address of a missing character. No worries. Python's index method is your Sherlock homes solving the case of the lost child in the string family. Let us take the string named statement that we have used in the previous sessions. If you are looking for the address of the character T, Python's index method is quick to answer. The address is index zero. What about IS? Well, Python doesn't panic, even if there are duplicates. It calmly follows the first come first sound policy. IS lives at the index two, no fighting over the second occurrence. Got it. Good. Python is great at finding stuff. Just don't ask it for something that isn't there, then it throws an error. Similarly, character yes is repeated thrice in the string. But the first occurrence of yes is at the index three. We are comparing the string Python with string having same characters, Python and cross checked if there is any spelling mistake. Same characters. But when you ask Python to compare them, it says false. Why? Because Python is a perfectionist who judges every uppercase and lowercase differences like a grammar teacher marking your essay. Google search engine, do not bother about the case of the search you have provided. Cannot expect getting the perfect input with the proper cases all the time. How can I ask the Python to ignore the case? If you need to compare the string, ignoring the case, then use case fold. Case fold is a liberal valuator who do not cut the score for silly uppercase and lowercase mistakes. It is the time to make some changes to the cases of the string. Let me define string for the case operations. I'm too lazy to find the variables and string. My variable name is string and the string is example of Python string. Why in the world should I bother to find the identifier and a string? Let us start the operation. The first method is capitalize. Capitalize will make the first character E of the example to upper case, and rest will be in lower case. Observe that P of the Python has changed from uppercase to lower case. If you do not like to discriminate the characters and want to treat all characters equally, use upper and lower methods. Upper will convert all characters in the string to uppercase. If upper method is understood, then I'm very happy to tell you that our time for explaining the method, lower is saved. In that saved time, we learn another method count. Do you know the meaning of the word count? You guys are making my job easy. The method count will return the number of occurrence of a substring. We shall use this method on the string with the name, I mean, identifier statement to check the frequency of the substrings. It says you are repeating the same substring like a broken record for this number of times. In this case, it is two. To next methods ends with return true if the string contains whatever it wants to be, but ends with a substring mentioned as argument. This will be useful in testing cases like if the string is a URL or an email ID. Testing the URL, www.abc.com, if it ends with.com, and email to check if it ends with some domainm.com. As both of these conditions are satisfied, it return true. Now tell me if you have understood method ends with. If you have not understood, then move video a few seconds back and see once again. If you really understood this method, then there is no need to explain start with earn one, get one free. Let us move on. By default, Python treat everything that is enclosed inside code as string. It might contain alphabets, numbers, special characters, and whatnot. Let us explore some methods that check the type of the characters in the string. First, let me define some strings to test the methods. As I told earlier, why we bother about identifiers, I name them accordingly. Numeric with numeric characters, Alpha, which contains alphabets only, Alpha numeric with combination of alphabets and numeric characters and special which contains special characters. Now we shall see the methods one by one. Es numeric. Check if the characters are numeric. It returns false if string contains alphabets or special characters. The next method is E short name of E alphabet. That is true if characters are among at Z or else false. Combination of Epa and numeric is isalnum. It returns false when the string contains special characters like ampersand, exclamatory, octothorPercent, underscore, and so on. Turns true if the string has alphabets or numbers or both. Do you still remember the lesson variables? Then recall the rules of identifiers? You can check the validity of the string that is if it is eligible to be used as identifier using the method, es identifier. Returns true if the string is a valid identifier. If it violates the rules of identifier, then it returns false. These are the test of type of characters. Now check the cases of the characters in a string. Es lower return true if all the characters are in lowercase ignoring numeric and special characters. Even a single uppercase will change the validity of the test to false. The sibling of this method is E upper where the case is true if all characters are in uppercase. These methods just check the conditions and return true or false. If you want to convert the characters to either uppercase or lowercase, we already learned the methods like lower and upper. Move on to next method. The sting is messy and has some unwanted things in it, then Python provides cleaning tool to remove the mess. Lstrip is left handed and hence clean the leftmost part of the string. Lstrip will check if the left part of the string contains the unwanted things mentioned in argument. If the case is true, then it removes them. If argument is not mentioned by default, lstrip removes the spaces if first characters are white spaces. In the example, Ylstip is provided with the argument ABC for the string email, which has value ABC at the red domain.com. As the email start with ABC, it removes it and return the remaining string. If you need to clean the mess in the right or the end part, then R strip is used. This works exactly the same as strip, but RStrip is right handed and hence hold the sponge in the right hand. For the same email example, RStrip is provided with domain.com. Python clean the right part and remove domain.com. Result is left with ABC at the right. If you need super efficient worker who can work in both hands to clean the mess on both the ends, use the method strip. Here, the string has unwanted white spaces in both the ends. We shall remove the white spaces, both at the beginning and the end using strip method. These triplet strip brothers remove the unwanted characters, make the string trim clean and save the storage space. Do you like to break the unity of the string? The strings can be broken into number of pieces using split method. Split by default separates the string into the list at the occurrence of space. The string in the variable statement has four words. This is a which are separated by spaces. By not providing any delmeter, string is cut into four pieces at the space to make the list of four words. If you want to split the string at any other delimeter than space, then mention it as an argument in this case, string is split at the occurrence of the character S. There are three S in the string. Hence the string is broken at three joints, making it into four pieces. If splitting or breaking the string is possible, then welding the string must also be possible. The reverse case of split is join. Join is virtual adhesive for the string. Join connects the list of substring into one string end to end. First, define the delimeter that separates each element. Here is a list of three different string and these three words are joined end to end in the order and separated by white space as requested. Congratulations, string warriors. You have unlocked the full power of string methods from cleaning, slicing and dicing to transforming and inspecting. Go out there and conquer your strings like the coding pro. By the way, are you feeling overloaded? Just practice the programs regularly and apply the concepts. You will use them effortlessly later. See you in the next session. 18. What is Functions & Methods?: After going through all those heavy loads of information, some or the other person would have left with one big question unsolved. From the long time, I was using these two confusing terms, functions and methods. What exactly is functions and methods? Are they relatives or enemies? I mean, are they similar or different? I thought of explaining this concept in the first module, but I don't want to give you just the scary definitions because definitions are by default designed to look scary. After learning to this stage, I have a lot of examples to explain you these two terms, it's good time to learn these two terms to the depth. You have already met and used many functions. The print help are all examples of functions. We have also used the functions for explicit conversions like Int, STR, or float. You must have realized the importance of functions coding. Programming without the functions is like trying to cook without the kitchen utensils. You end up steering the soup with your hands. Now comes the question, who is eligible to be called as function? Wear your seat belt, I'm going to give you the definition of function, and I know very well that these definitions almost always create turbulence. Here we go. Functions are the set of instructions that perform a task. Functions do not change the parameter, but they return the new version of it. Who cares those boring definitions? Let us understand through the example. Variable string contains the string data, and hence, let's consider length function. Function always start with the function name followed by the parameter in the parenthesis. The definition we set, it performs some task. Yes, length function find how long the string is, not in terms of meter, but in terms of characters. Consider one example of list. We should just see how functions work. LSD is list of some numerical elements. I use a function sorted, and I will assign the result to a variable sorted list. The task of this function is to sort the values in ascending order. While defining, Sone also said the functions do not change the parameter but return the new version of it. You check the initial list LSD, it don't even have any clue or idea that you have sorted it. But new sorted list has got new version of the LSD. Functions are the tools available in Python that are always ready to serve you with love and waiting for you to use them. They can be used anywhere in your code just by calling their name. Now let's visit another friend method. As usual, like everything, let's start with definition. It says, method is set of instructions that are associated with the object that can be used only for that specific class. I don't know why these definitions are always scary than they actually are. For the string, you have learned many dot notations like capitalize upper case fold, start with, ends with, and so on till infinity. All these dot notations have the fancy name called method. Let's take the example of is numeric. You know very well what it does. If I use the same method with the integer values, what will be the observations? You'll get the attribute error with the message. It object has no attribute is numeric. Method is racist, which is specific for particular datatype only. That means method of one datatype is not compatible with the other datatype. This is what said in the definition, methods are associated with the object that can be used only for that specific class. Dot notations of string will not available for other datatypes. Let us see why the term class is used here in the OOP session. Don't worry much about it. You will understand that later. As of now, it's good enough. I hope you have understood the difference between the functions and the method. Let's forget methods for few moments and concentrate on functions. Only for a few moments, not permanently. Built in functions are baked in the restaurant of Python for you. You just need to go to the Python restaurant and order any function you need. But sometimes the dish you are looking for is not readily available in the Python restaurant, no, online order will not work here. That is the situation where you need to cook your own functions. Such functions prepared by yourself are called user defined functions. Are you exited for the cooking session? See you in the kitchen. 19. Defining Function: Till now, we have mastered many Python built in functions, especially on string. Python has several built in functions, serving various use cases and tasks. Some of them we have already went through and some of them we are yet to explore. But these functions might not be able to solve all our required tasks. We cannot expect everything as per our requirement. What we shall do in such cases. In the ancient days, humans use stones and sticks for hunting. But is there sufficient for all situations of hunting? No. When the existing tools are not efficient and sufficient to fulfill our needs, humans used existing tools to prepare arrows and other sharp tools, which made our work a lot easier. When we do not have what we need, use what we have as the raw material and create the customized product. That quality made humans unique among living organisms. Similarly, we define the functions as per our requirement when we don't have one. Such customized functions are called user defined functions. User defined functions is similar to teaching new recipe to the Python using the ingredients we have so that it prepares for us whenever we want as per our instruction. Let us say, we need to calculate the area of the circle. We don't have any ready functions to do that, so we are teaching the Python this new recipe. Type def. No, Python is not def, but it is the short form of define DAF. This is like telling the Python, Hey, Python, the built in functions you have provided will not enough for my task. I want to define my own function. Python says, Okay, go ahead. But what is the name of your function and what input you need? Now provide the name of the function that is understandable along with the input parameter. Recall the rules of selecting identifier. As name of the function is also an identifier. Rules are valid here. Accordingly, I name my recipe area of circle separated by underscore, as identifiers dislike space. To calculate the area of the circle, the required parameter is one that is radius. You have defined the name of new recipe and also required ingredients are also listed in the form of parameters. What's next? To bake and prepare the recipe. Start giving instructions how to bake. As all the code I'll be writing hereafter belongs to this function that is explaining how to prepare new recipe, provide a colon telling Python continuation of this task. Now you can observe indents have been moved. Once this function is defined, you just come out of this mode indents to end the function that we shall see later. Now provide the expression to calculate the area of the circle. Area is equal to pi times radius squirre. Now our recipe is prepared and we need to present the prepared recipe. What is the output of this function? It's area. Return area. As you provided written statement, Python understand that your cooking session has ended. I mean, the function has ended. Hence indents moved back. Now your function is defined. What shall we do with this function? It did not return any output even after executing it. No program know what to do. What it don't have is input value, the radius of the circle. How can it return output without input value? No ingredient or recipe. You have just taught the Python how to prepare the new recipe, if you want the Python to cook as per your instruction, you need to order it to do so by giving the ingredient. Now calculate area using the function by just providing the radius, which is the only and main ingredient of this recipe. Now you've got the output. This is an example of single parameter, single output function. You can define multiple parameters and multiple output, like in previous example of area and perimeter of rectangle. This recipe has two ingredients, length and breadth, unlike one ingredient in area of circle. Ingredient list is separated by comma. Using length and breadth, we make area and perimeter. Recipe has two outputs, written both area and perimeter. Both parameter and output need to be separated by comma. This recipe is taught to the Python. Now use the defined function and provide with length and breadth. You get two output, 601 hundred. This is always in order we provide in written statement, area followed by perimeter. In function, you define the rules once and use it multiple times. The output need not be written always. It can also be print statement. The same example, function to calculate area and perimeter of rectangle is written with the print statement. Output looks similar. Both this written and print statement give the same or similar looking output, but they are different. Print statement display the output, but its value cannot be saved or stored or further used for calculations. As written gives value that can be assigned to the variable and can be used for the further calculation like we did in this case. Area and perimeter are calculated for provided length and breadth and resulting values are assigned to two variables. That cannot be done when there is print statement. Hope you have got the difference between print and return. In the next video, we shall explore a few examples of functions. See you there. 20. Examples of functions: In the previous lesson, the concepts of user defined function are discussed. When we need to program the routine task, we can use functions as they can be built once and used multiple times. In this unit, we shall see a few functions so that you will understand the concepts of functions better. Functions can be as simple as this example. Greet which take the name as input and print the statement hello with the name. Now use the function with the name here, John. Look at another example, Celsius to farnate as the name suggests, the function for the temperature conversion from Celsius to fnate. First step, give a beautiful name for your dish and mention the ingredient. I define function name with the temperature in Celsius as the input. Do you remember the formula for conversion? If not, Google it or ask ha GBT. They are the only teachers who can help you at anytime with any problems. Let's come back to our formula. It is temperature infarnate is equal to temperature in Celsius multiplied with 1.8 and add 32. Now return temperature infarnate which is our end result. Now I use function Celsius to farnate with 25 degrees Celsius as input, which is translated to 77 degrees farne. Let us make the program more dynamic. I'm not entering the value here. I'll get the input from the user and convert it to float. Now enter the value as a user. It returns the converted temperature. But we are experiencing a long decimal part here. If you want to restrict the number of decimal points, add round function in written statement. As the name suggests, it round off the values and I'll be limiting the decimal values here to two. Use round function whenever you like to have. Now let us run the program again. We got it. Isn't it cool? Learn the concepts of user defined function well. We are ending the model here, but our friendship with the functions will not end here. It will continue till the end of programming journey. Every now and then they will appear. We use them very frequently in programming. Even you get your hands into various functions of your liking. Create functions to solve your day to day task. You will get practice easily. Also, it will help you to program efficiently. Now we shall take some rest and meet again in the next module. 21. Conditionals and Branching: Do you still remember the comparison operator? Congratulations. You don't need to watch it again before going through this module. There we have compared the values to get the result in terms of true or false. What we should do with true or false? Even kids will answer that, true or false. We need to make some decision based on the result of comparison. That's how we make decision in day to day life. What if the day is rainy? If it's true, carry umbrella when you go outside. Else, if the day is sunny carry protective eyeglasses. We make this I and s analysis. Now bring them to the programming and apply them to an example now. This is a program that will decide what gift you get to go to college based on the score you got on exams. Let us provide their score they got on exam. If they want, add the statement like enter your exam score. Now put the conditional statement. If score is greater than 90, as discussed in the previous module, this statement has not ended, so provide Colon saying, Python, hold my seat, my journey will continue in the next line. So if your score is 90, you get car to go to college. Assume you are a rich kid. Now, what if this condition is false and kids score less than 90? We have a backup dancer in the party. If the first answer, I mean, condition is true, then it is great. We can make them dance in the party. But if they did not turn up and answer is false, we shall have the backup dancer in the form of ALIF and s, who is the last option. We shall see them now, ALIF, which is the short name of s if score is above 80 and below 90. As above 90 is screened in the previous statement, I don't define the statement greater than 90. Otherwise, you include the statement. Here it is not necessary. If value is above 90, who is the main dancer? The code neglect all the other part because they are just brought as backup. The program will conclude by executing the first function and directly come out of if statement. Let us come back to our second condition. If score is above 80, you get a motorcycle. Not bad. But what if the score is still less? If score is below 80 and above 70, the gift is bicycle. If you want to save enronment, score 70-80. Come to the last case, se, we are using se here, not F because this is the last backup dancer and we don't have any other backup now. So we use se instead of LIF as it is the last condition. If score is below 70, you get nice pair of footwear so that you can walk or take public transport to go to college. If you want to stay healthy and fit, score below 80. Do it at your own risk because these conditions may not apply to you. Don't tell me your dad did not gift card to you despite scoring 90 plus. Even my dad didn't. Just like the conditions, the output can print something or return some values. If you need to use the same program multiple times, bring them inside a function. We shall use that right now. I include these conditional statements within the function. Say decide gift is the name of the function and exam score as argument. Everything else remains now use the function to get the output. Conditionals can be used independently without functions. With the conditionals, the user defined function get more power and versatility. For some use cases, IL statement can also be used in single line. If you are lazy, then might have excited to learn how. Then stop this video and jump into the next one quickly. 22. Examples of Conditionals: A we shall see a few conditional examples. First, we start with very simple examples of conditions within the function. It is a function that find if the value is even. As usual, I define the function, DEF is even with the number as parameter, and now experience the beauty of Python. Next one single line will take you to the climax. Return true if number modulo two, which means the remainder when number is divided by two is equal to zero, se false. Python understand human like language. Test few more cases. Here you can see the close relative of the previous function, which written if the number is odd or even. Only difference is earlier output is Boolean. Now it is the string, odd or even. Write function name with a argument. Then written even if number mod two is zero, se odd. Why always numbers? String will be angry, and we treat everyone equally. Time to take string as an example now for argument. Say there is some statement like this. Python is a programming language. Nothing new. This statement is an already known fact. User want to know if there is a particular keyword in it, say Python. Define the function with string and substring as argument. Return true if substring is in string, Ls false. This statement literally feels like human language. Even someone who do not know programming, but know English can understand these lines. Make some modification to the substring now, making P to the lowercase. But remember, the string is case sensitive. If Python is in lower case, the story is different. If you don't want to be case sensitive, use case fold method that we have discussed in the string module. Now last example. All this example we have taken are written statement. Print statement will feel bad as we are using the written for all the examples. Here is your example, print statement. This is a simple program that return if trade is profit or loss, along with the value based on bought price and sold price. Define name accordingly, along with bought price and sold price as arguments. Now, outcome is defined based on which value is higher. If bought price is greater than sold price, outcome is loss, otherwise, outcome is profit. Now comes the print statement, which print the outcome along with the value of profit or loss. Value is found by the difference between the bought and sold. But here the value is surrounded by several layer of parenthesis. What a tight security for difference between bought and sold. Let us understand them layer by layer. Start reading from inside. First, we need to calculate the difference between bought and sold in both case, whether it is profit or loss. But if the bought price is lower, the value will be negative because it's loss. As we have the outcome printed separately, and hence we need to ignore the sign of values and take absolute. If the value is negative, it return as positive value. If it is a positive, absolute has nothing to do. I can chill. Once Absolute has done its work, value is converted to string so that it can be added with other strings. Here, dollar is used as a currency symbol. Add whatever you want if your keyword allows you to do so. Now continue statement with outcome which has value, profit or loss. Now function is ready to use. Great. Oh, forgot to check. Are you still with me or sleeping? I understand. I will end the lesson and give you free time to really take rest now. 23. Loops: Have you ever felt bad doing the similar routine task every day? Most of the professionals do the same or similar things every day, which we the humans feel mundane after a few months. Computer is better at doing such task because it is a machine, do not have any emotion and never feel frustrated. Hence, it can do same boring task million times without complaining. The loop is the term used for repetitive task. We all have experienced such routine mundane repetitive task. In programming that is achieved using loops. Loop is a set of instruction that continue to execute repeatedly till some condition is violated. Let us make it simple to understand. It simply means loop is a strict pause who do not leave you till the task given is done. Loop is programming version of your school exam. There is no escape from it till the exam is passed. Till then repeat the same procedure. Now let us find real world programming example of loops. Do you know ATM machine? Sorry, I know it is a wrong question. Who don't love the machine that gives money? How does it work? First step, user enters the amount he needed. Now system enters into a loop and in each loop it returns currency and value is added to total amount collected. Machine keep on to dispense the currency till the total sum reach the amount requested. Once the amount is equal to requested sum, machine comes out of the loop and release the currency to the customer. Did you understand the concept of loop or entered the loop of doubts and questions? Don't worry. By the end of this module, you will come out of that loop of confusion. There are two types of loops used in programming, I loop and for loop. Imagine you are making sandwiches to your entire family. I'm sure you will not keep on making hundreds and thousands of sandwich, preparing whole day. There must be an end to your task preparing sandwiches. There are two types of end to this task. Number one, you must stop making sandwich when all the bread you have are exhausted. Second type of end is when you have made enough sandwich that all member of your family, including you are satisfied. The first case is for loop. In that case, based on the number of bread you have, you know how much sandwich you are going to prepare. The second case is i loop. In yoop case, we cannot calculate how much sandwich you need to prepare. Someone may have one, some might take three. You need to keep on preparing till everyone had enough they want. This is silly difference between for loop and i loop. We shall see them in detail in next video. 24. For Loop: Now it is understood that loop keep on executing same set of instructions for multiple iterations. Statement sounds good, but the term multiple iteration is very general. Precisely, how much iteration is that multiple iteration? For some use cases, we know how much iterations program should go through the loops. In some cases, we do not know the exact number, but keep on executing until certain condition is violated. There are two types of use cases. If you or the program know the answer for this question, number of iterations, then such use case is four loop. Before you join the college, you know how many years you need to pass to complete your degree. Similarly in for loop, program no the number of iterations it goes through. You will use the four loop in your kitchen too. Imagine you are a chef and need to peel the potato. You pick one potato in each iteration and peel it. Then you go for the next potato. Before you start peeling, you know how much potato you need to peel and in each iteration, you know how much is left. I assume your concept of four loop is clear. Of introduction, we shall see the four loop in action. Here is the simple example of how to define the four loop using the range. Define the range by mentioning start and step size of the range. I hope these terms are not strange for you if you have learned the string properly. Aren't you happy? Your old friends were back? Like in string, if you miss any argument among start and step size, program assume the default value, but the last value of the range is strictly defined. When you are informed that your chef has peeled four potatoes, then you start counting from five. But when you don't have any such information, you start from beginning that is one. But for Python, start is zero. Hence for Python by default, range start from zero in the step size of one till the last value minus one. The range five indicates 0-4, that is N minus one or five minus one, which is four in the step size of one. Range five is zero, one, two, three, and four. Is assigned to I in each iteration. Nothing complicated here. We are taught or learn to make things complicated. Just like you pick one potato each time to peel, loop take one value in order and enter the loop. That is, in first iteration, I is assigned zero and with the value, I enters the loop. In next iteration, I is assigned with value one. Now the program says, I understood what are the values with which I need to iterate. Now tell me what I need to do in each iteration. It is the time to give the instructions what to do with the range. Example, here, print I squared. If you execute this, in the first iteration, value I is assigned with zero, it calculates I squared, print the value, and go to next iteration. That continues till the last value of I, that is four. Once all the potatoes are peeled, program comes out of the loop, you are left with a set of peeled potatoes that is I squared. The peeled potatoes looks like this result of the square of range zero to five. Do not like the plane output, you can add statement like square of the value is this. In this example, start of the range is not defined and hence by default, it assumes zero. Now we shall define the range which start not from zero. I will define five to ten. Someone has already peeled four potatoes. Hence, you need to start from five. Now can you think of the values that goes into the loop? It is five, six, seven, eight, and nine, but not ten. I will not make any changes to the value and print the values as it is, print X. It is very simple example. Now climb one more step. Now define the range with the step size. In the previous module, while understanding the functions, we have defined function for Celsius to farent conversion. Now I bring the reverse case here, farnet to Celsius conversion for the next code. Temperature in Celsius is equal to temperature in farnet -32, whole divided by 1.8. Return temperature in degrees Celsius rounded to two decimal points. Now function for our calculation is ready. Come back to the four loop. I am defining a range from -50 to 50 with a step size of ten. If second argument is 50, the range will end at 40. If you need to include 50, you can define 51 instead. Now print the value of degree Fahrenheit and corresponding degree Celsius using the functions. Here, output is calculated not for one particular value, but for multiple input values, and users do not have the hassle of providing several values to the function. We are pampering numbers so much that string might feel jealous. In the next example, consider the letters in string Python. For letter in string carries each character to the loop in each iteration. I will print the characters one by one. This is a simple example of the string. We shall try the four loop with data structure like list. As the first step, define the list. If you do not understand what this list is, then don't scratch head. Going to learn about them in detail in the next module. Here we provide the list for the iteration using the statement for fruit in fruits. Fruit is variable assigned to each iteration, and fruits is the name of the list. In each iteration, one element of the list in order is carried into the loop. I will print some statement which sounds similar like I love and add variable fruit. I don't know which fruit you don't like because neither I know you personally, nor I am a mind reader. Let us assume you hit pineapple. I add the statement if X is equal to pineapple in the next line, adding keyword continue. What it does is it skips the print statement if fruit is pineapple, otherwise, print as usual. There is one more similar keyword, break. Using the break in the loop is similar as continue, but break will stop the iteration when some condition is satisfied. When the condition is met, loop will be upset and will not continue further. In previous example of fruits, if the fruit is pineapple, continue will skip the pineapple and continue with the other fruits. Break is used, programs stop consuming fruit when it find pineapple and the loop stop iterating, we shall see the example of using break in programs. We use electronic gadgets which are protected by the password. The gadgets ask to re enter when the password is wrong till maximum attempt is reached. It is an example of a loop. Once you enter the correct password, it breaks the loop. Now we try to understand what is happening in this example. First, I define the actual password. I know password cannot be displayed so openly, but it is just an example and here we are just understanding the concept and do not think this is my password. I'm smart enough not to keep this simple password. Define the conditions. I define range five because five is the maximum attempt for this case. Ask the user to enter the password using the input and get attempt password. If password entered is correct, then interface should print correct password and break the loop. Here, break is important. Otherwise, program asked to enter the password five times even if the password is correct. If the password is correct, this loop is to be broken. Else inside this, there is one more condition. If I is four, that means the fifth attempt as I starts from zero. Give the message that attempt has exhausted. Otherwise, ask to enter the password again. That is simple to understand. We shall execute the program. Test the program for the use cases. First attempt failed, tried again, and in the third attempt, I entered the correct password. Program now don't ask me to enter the password again. Great. Let us go one step forward in for loop. It is time to use loop within the loop, which is called nested loop, but we shall see them in next video. 25. Nested For Loop: Nested loop is like onion of loops. Once you break the first layer, you have a surprise. You have one more layer. As a beginner, if you see several layer nested loops, it will cause headache. Hence, we try with two layer nested for loop. First, we shall understand the use case. Here I'm making list of all possible tournament match pairs among the teams for being unbiased and easy availability. Have named team as ABCD, E and F. We have full freedom to name the team as you want. No one will ask us and also do not ask me which game. Again, I give you the freedom. You can assume any game that is up to you. I have defined the team's name. This type of collection of data is called list. Now start the first for look for Team one in teams. It will select one team in one iteration, starting with first team. Now we need to select one more team to play against the first. Hence, we use the nested for loop to select the second team holding the first team in hand. Team two in teams. Now comes the condition. There are two conditions. First, as nested for loop, do not know that we are selecting the two different team to play against one another. It will select the same team twice. Team two should not be same as Team one. Simple logic. They cannot play against themselves. Second, once a pair is formed, that pair should not repeat. What that means is once pair, for example, A and B is formed, then no need of another pair, B and A. I will target both these conditions in one statement. That is index of Team two should be strictly greater than team one. When it is strictly greater than, there is no possibility of having the same index and it won't repeat the previously formed pairs. Now print Team one versus Team two. That's cool. Such type of four loop inside another four loop is called nested four loop. Now we shall see one more example that was nightmare of our childhood. Do you remember the multiplication table? Using the nested four loop, we can create the tables in just four to five lines of codes. Are you excited? To create tables, we need two values in each iteration, and third is the product of first two. Hence, we define 24 loops, first four loop, for I in range 126, I'm creating a small table till five multiplied with pi. If you want, you can make larger, but the logic remains same. Second, similar for loop for J in range 126. There are two values I and J. Print in the format of tables. I and multiplication symbol, I use X, and value in J is equal to the product of I and J. In format, mention I, J and value we get when I is multiplied with J. After one set of J iteration, let's have one blank line for better looking. That's it. We are done with coding the tables. Execute this code. You table is ready to serve. Interesting. You might have understood the importance of nested for loop. It makes your complicated codes very easy. Let us say meet you soon to the for loop. If you find for loop easy and interesting, then you will feel it easier with the Y loop too. 26. While Loop: In for loop, the number of iterations is known based on the range or the elements of sequence. Met new friend yoop. I loop is like dancing in the party which has no time restriction. You will continue to dance till either you feel tired or guests in the party start leaving. In yoop, iteration is based on some condition. Here is a programming example. Let us start the i party. Now the first song is being played for you to dance. I will assign the value one to a variable X. Let us say you will be exhausted after dancing for six songs, that is your limit. I want to set the value of X. The number of song that is played is set less than six. Write that in the language of Python as while X is less than six, I will give some operation here, say your tiredness gets squared with each song you dance for. Square the value of X like we did in Flo. Let me explain what the program will do now. Python know the value of X is one. Y loop will check if the value of X is less than six. Unless computer has any learning disability, value of X that is one is less than six. As this condition is true, the loop is entered for the first iteration. As per the instruction in the body, program print square of X that is square of one. That ends the first iteration of loop. Now the program goes back to the Y loop condition and check if the condition is true again. The value of X remains one as the party organizers won't come and update the song number, which always remain less than six. Did you observe an important thing here? This condition is true forever unless the value of X is changed. As this condition never changed by itself, the program keep on executing infinite number of times, wasting the resources, and finally hang your computer. That is the reason y loop is bit dangerous as number of iterations are not defined. How can a value change itself? No, it won't change itself. They always need a statement inside the Y loop to change the condition that y loop checks. Here we shall add one value to X in each iteration. That is X is equal to X plus one. In first iteration, X is one. At the end of first iteration, X is incremented by one unit. When I loop condition is checked for the second iteration, the value of X is two. At the end of each iteration, the value of X is increased by one unit. Now there is a situation where X is equal to six, which violates the condition and the far loop stop iterating. Now execute the program. Perfect. Infinite loop is the major concern of Y loop. Now look at this senseless program. This condition has the statement to change the values that is X is increased by one value. Still, X will always be above zero. Here also program always remain true and hence it cause infinite loop. Just make sure while program, ilop will not end up with the infinite loop. Otherwise, you need to keep on dancing day and night without break. Now let us see how we should deal with the string. As the first step, I will define the string Python to a variable string. Let me explain the use case. What I'm doing here is I will print each character separately like we did in for loop. We shall define the index, which is initially set as zero. As index cannot be greater than the length of the string, I will define while index is less than the length of string. Now print letter include the index in the format of index plus one. As we don't count the character from zero like Python. Along with that, print the character of the string in that index. Now important part, give increment to the index before it reiterates to the loop. If you do not know it, index plus is equal to one is same as index is equal to index plus one. Program is ready to execute. Looks good. We shall look at the example of how to deal with the list. Here is a list of numbers and in the current example, we shall develop the program to compute the average of the list. Define the variable index and assign the value zero to it and create another variable, say total, which is also assigned with the value zero. To add and store any ingredient in the box, the box should be first empty. Hence, the index and total are assigned with the value zero to make them empty. Oh, why no one has told me yet. I cannot use the name list for the variable as list is a predefined keyword in Python, if I need to use the name list as the name for a list, I need to misspell it LSD. Now I don't have the hassle of finding the new variable. Now comes the Wiloop condition. While index is less than the length of the list, this statement ensures that all elements of the list went through our Wile loop security check. Write the code for the body of the loop, find the sum of all the elements of the list. Total is equal to the value of total in the previous iteration plus element in the index. Now important part that we have to remember for the Y loop example, increment the value of index by one. In first iteration, total is zero, which get the first element added to it. In each iteration, total adds the one value of element to it. Once it completes all iteration, total get added with all the element which makes it sum of all the element, as its name suggests. Now comes the climax, calculating the average using the total. The average is equal to total divided by the length of the list. Program is set, you can execute. Hope now you have understood the difference and application of While and for loop. In the for loop, you have seen the application of break and continue functions. While loop entertain break and continue functions just like for loop. I know just mentioning will not help you. To understand the concepts, you need examples. Here is an example of break function. As functioning is same as the one we used earlier, I don't repeat it like the broken record. I plus equal to one is same as I is equal to I plus one. Similarly, try with the continued function and get the answer. If it is same as you guessed, I assume your concept is clear. That's interesting. Loops are important part of programming. Hence, practice it more to become confident in programming. For now, take rest and let's meet in the next module. 27. List: I hope you're enjoying the journey of learning so far. Most of the concepts you have learned so far are so easy and similar to the ones you have learned in your schools that bring you the memories of early school days. Let us now go through another primary school concept. When I said primary school concept, I'm sure you are filled with the enthusiasm and excitement along with your old memories. When we were kids, we had these type of questions asked in the exams. List A five fruits, list any four mammals, simple quotiens for which we used to write few examples of members belonging to that category. Now we shall learn same concepts in programming terms. List, as its name suggests, is group or set of data assigned to a single variable. The elements of list are included inside the square bracket and are separated by comma. Here are some examples of defining the list. List is not stranger for us. We have met list earlier in various models, but we could not get the complete introduction of the list. It is the time to know about the list. The first list fruits, as its name speaks, everything is the list of fruits where elements are of string data type. Primary number is a list with elements belonging to integer data types. Class core is a list of marks scored by kids of the class, which is floats. Don't ask me if the class has strength of only four. This is for understanding. If you have time and patience, fill the score of whole class. What we can observe here from this example, user has all the freedom to use elements of any data types in the list. There can be string, numeric, even mixture of different data types, and also can be list. This list of list is called as nested list. Did you take the notes on the operations performed on the string? If yes, your effort has reduced a lot. Go through them once and recall. Most of the operations we performed on string are free with the list too. But why operations of string have few common with the list? Because they are close relatives. Just remember one common relationship between string and the list. String is the collection or sequence of characters and list is the collection or sequence of elements. This similarity makes the few operations common between string and list. Which are those operations that are common for list and string? It is the right time to explore some of them. First example is length. In string length function LEN returns the number of characters in the string. The same alien function is used in the list which return the number of elements in the list. Next operation that comes free for the list along with the string is adding two or more string, which concatenate, that means joins them end to end. Similarly, adding two list will join the elements end to end. The other common operations between string and list are indexing and slicing. In list, the concept of indexing and slicing will be same and hence I will not waste your time by repeating the same things. But look at these examples. You will understand how to use them in list better. Slicing is easy for list once you understand the string, but list comes with some twist. Do you remember about nested list? We just said, excess in data might seem a bit confusing for the nested list, but it is not. Excess the element using two indices. For example, list zero, one, which are included in two separate brackets. Let us understand this with splitting. First, we select zeroth element or which is the first element in human language, which is, again, the list. To further explore, I provide the index of the nested list in separate bracket. So I'm accessing the element in the position, having the index one. Isn't it simple? It is simple and straightforward. Okay, we saw the similarity of list with the string. They are relatives but not identical twins. There is one major difference between operations on string and list. That difference is list is mutable over string. I know that word don't sound cool, but its meaning is very simple. List is very flexible. It just means that you can add, modify, and remove the element in the list where the characters of the string cannot be modified. We can only assign a new string to the same variable. Let us explore those mutation advantages available for the list. Take the fruits list. Some lazy fellow has added only few names to the list. Now the same lazy fellow will add few more elements. I use append function. Append function is the security at the entrance who allows permitted person to go inside the list. Append will add the new member at the end. I have run the line twice by mistake. Hence mango is also added twice. Mistakes teach us many things. Even with the mistake, we can observe and understand one thing here. List can accommodate duplicates. A pen has a bad habit, not really bad, but we can say limitation. Even if the new element fruit you added, mango is your favorite one. Python give last priority to the new element. It gives first priority to seniors. To add the element to a specific index, we have insert function which takes two arguments, one index and second element. Element is added at the specified index and move the other elements on the right side by one index. What if the specified index is greater than the maximum available index? I know you get such creative questions. Simple, it adds to the end. Opposite is also true. When specified index is smaller than the minimum index, it add to the beginning. Right to add the element also gives you the privilege of right to remove the element using the remove function. Remove function need element as argument. You can also remove elements using the index of the element. To remove the element based on the index, pop function is useful. I removed one mango, remove function, take element as argument and pop take index. When pop don't have argument, it remove last element. Pop does one more job. While it removes the element, it returns the value. What does that mean? Simple. Element kicked out of the list using pop function can be assigned to a variable. Now let's explore ordering method in list. As I told in the beginning, Python is so beginner friendly that anyone can say what a function does. Here are a few examples. You can see two functions used here. One is reverse and one more is SAT. Both of these are well known English words, so I hope you know the meaning of them already. Just guess what they do to the list. Guess it correctly. Thanks for making my job easy. You can compare the result before and after. That is made directly in the next lesson. 28. List Comprehension: In the previous lesson, we saw list that is defined by the user by entering the elements manually. If the list is large, it is quite difficult to define. Moreover, we are lazy that we always find some easy way to do the task. Python know we are lazy to even enter the elements. Hence Python can create the list with the elements for us if the elements are based on some rules. If you want to create the list that are following some pattern, tell Python what you want as element in list and its condition, Python will make the list for you. We can define the list by giving the instruction that Python can understand. The statement must include what to do for what values and what's the condition if there is any. Here is an example. First, what to do. The instruction says to create a list of squares. Now comes the second part. Okay, we shall create the list of squares, but we can't create it from zero to million, right? Then for what values? This part says for I in range zero to ten. Is there any condition along with this instruction? Yes, consider only odd numbers. I I modulo two is equal to one. When divided by I, if reminder is one, then it is odd number. If your instruction has completed, then close the bracket. The condition part is optional. Here is one more example. X for X in range zero to 50. If X modulo four is equal to zero, and X modulo six is equal to zero. That means divisible by four and divisible by six. This example has two conditions combined by and operator. Hence, if both conditions are satisfied, then you get the value in the list, otherwise, skipped. We treat everyone equal. Next example will be for string. Letter for letters in Python. Here, the four loop, it reads through the characters of Python and add them to the list. This method is efficient when the instructions are simple and could be defined in one single line, like what are your favorite toppings for the pizza? When your pizza is to be customized as per your liking, that cannot be explained in one single line. We need to create an empty list and append the values to the list based on the instructions. Shall discuss this automated development and modification of existing list in the next session. 29. Automated List: We all dreamt of having the character like Ginni from Aladin in our real life. Who could do all the work for us. But later we accepted the reality. That is not practical, but it is practical to automate our programming task in Python. One such thing Python can do for us is it can create the customized list for us. Let us understand the automated creation of list based on the instruction using an example. In this program, creating the list of all the prime numbers till the provided number say N, it is difficult to define it in one single line like in previous session. There are multiple ways you can achieve the problem statement, so you can try your own method. I will be writing the program in two phase, first, developing the function to check the prime numbers, and in second phase, creating the list of prime numbers. I will start the phase one program to check the prime number. Name of the recipe is E prime and ingredient is one that is say number. Step one of phase one. Let us neglect all the values less than one, zero and negative numbers. If that is the case, written falls. Now test of primality is checked for all the number above two. I assume you have learned in school that the primality is tested only till square root of number. Square root is rounded to the next integer plus one is because for loop neglect the last value and consider till last but one. With the value assigned to I enter into loop. If I divide the number, then the value is not prime, hence return false. If the number has defeated all the conditions above, then it is a prime number and hence return true. Now the phase one, developing the function has completed, and I'm testing the function for random number 99. Got the obvious answer. False. It is not prime. Now second phase, developing the list of prime, creating the function print prime, till the value N, create an empty list for the Python to fill the elements. Prime numbers in the list must start from two till the value N. The value N might also be a prime number, which will be neglected by four loop, hence considered till N plus one. In the previous developed function, test if the iteration value a prime. If it is a prime we are searching for, then do not leave it. Put it into your basket by appending. If not, let it go. Once all the iteration is completed, basket is filled with the prime numbers. Return the prime list. Phase two is also completed. Now I'm taking the input N from the user till which the prime number will print. Now execute the function. You can also modify the list using instruction. Here is a list of Email IDs belonging to some employees of an organization. We need to update the Emil IDs with the new domain name of the organization. Don't ask me why we are not poking nose in organizations internal matter. You can assume organization has merged or anything, I have given you the freedom. What we are supposed to do is replace the old domain with new domain. Name remains same. Create an empty list to fill new email ID. I read through each element in old email list. Replace the old domain with new domain and append the new email to the list. That's it. Your work is done. Print the new email list. These are the methods by which you can create and modify the list using the instructions. I hope you enjoyed it. You can save a lot of time and effort of creating the list. That is something we the lazy beings love to have. But there are use cases where user must create the list, how to get input list from the user. We shall discuss that, but take a break and join the next lesson. Be quick. Don't take more than 10 minutes break. Otherwise, I won't allow you inside the glass, but you can apend yourself inside the next session. See you there. 30. User Defined List: Now you know how programmer defined the list and Python create the list based on the instructions. But in some use cases, user must have the authority to define the list. It's time to see an easy but very useful syntax for coding that is user defined list. I don't want to give you a brief introductory speech on the topic at the end of which you agree what I said, but knowing or learning nothing. Let us learn this with an example which help you better. You are now very familiar with the input statement. Earlier, we use the input statement to read a single value, which are assigned to separate variables. Now it's time to push the limit of the input statement. Now we shall assign a list of values to a variable. First, understand the use case. Nothing complicated, a new version of the old concept you have learned already. What the example will do now is ask the user to enter the multiple values. In other words, user defined list separated by space. The problem statement is finding the average value of the user defined list. That's it. As user defined list is the highlight of this story, let us keep it as climax. Now story begins. Recall, in the Y loop session, we have created a program that calculates the average of the list. Based on the same concept, we create a function to return the average but using for loop. Find the function average with a list named group as the input. Create a variable total and assign zero. In four loop, no need to define the index. For easy calculation, I will find the length of the list and assign to separate variable for I in group, which take each element in the list group into the loop in each iteration. And add the value of the element to the total. In the next line, move the indens back, which gives the message to the Python that this part need to be executed only after the for loop iteration get completed. Once the iterations are done, total is sum of all the elements in the list. Using the total, calculate the average and return the value. Now function is ready. Jump into the main part of getting the user defined list. User need to mention the number of test cases to ask how many list you will enter. If the test case is four, the program should ask the user to enter four list. How to achieve that? We already have met the friend who can help us to do that for loop with the test as range. But hey, why are you using underscore as the variable for the iteration? Are you so much lazy to find at least one letter to define the identifier? It's usually done when the variable of the iteration is used only for keeping the count and there is no other significance in the program. That is, its value is not used inside the loop. This movie is very small. We have come to the climax. User defined list. Get the list from the user as input. Is it feeling scary? I can understand, but it is very simple. See how it works from inside. Input statement, as usual, read the input from the user. You know it already that input read all entry as string. User enters the list of numbers separated by space or any other delimiter. Input treat the space separated values that user enter as one string. Do you remember the old friend split from string operations? Input string is separated into individual values using the split. Map function make all the element into integer and feed the values to the list function. The space separated integer values are mapped into the format of list. Important thing is user need to enter the values separated by space. Any other delimeter like Coma is to be used, mention it as per the rules of split that you have learned in string. I give it as homework for you. Then calculate the average of values entered using the function recipe that we have already defined. Program is ready to serve. I'm testing the code for the four use cases. Python will not leave me till I enter four list. Be very careful in entering the test cases. If you provide 100 test cases, God bless you. Number of elements in each list is user's freedom. I will be providing five values each. It returned the average and asked me for another list. Once I enter four list as use cases, program has stopped asking me the values, allowing me to take the break. This time, I will take a quick break and join you in the next lesson. In the next session, we shall see someone who looks similar to the list Tapal. We shall meet Tuple learn it similarities and difference with the list in the next session. 31. Tuple: I Tapal is the brother of list who is bit strict. Tapal is a sequence of elements that are very much similar to its sibling list, but Tapal is immutable. They cannot be modified and their positions are stable. Once the list bag is packed, anyone can add or remove the things from the bag. But when the tuple bag is packed, no one can modify the packing, it's sealed. Even the creator, I mean, programmer who defined the tuple has no authority to modify a tuple. Only thing he can do is he can replace the old tupel with a new one. List and Tapal look similar, how tuple is differentiated from the list. The visual difference between list and Tapal is tuple is packed inside the parenthesis, unlike list, which is inside bracket. But functionally, there is much more to it. Take an example. Name of a person is to be stored in the form of first name, middle name, and last name. Their order must remain same to make better sense. If it is stored in the list, someone who has just learned the program and in experiment phase may sort the element alphabetically, which might make the data useless or meaningless. We cannot add, remove or even reorder the elements in the tuple. If reordering the element will alter the purpose of sequence, tuple is preferred over last. You have unknowingly encountered the tuple before. In function module, we have developed some functions that return multiple outputs. The output of the function is collection of the elements in the form of tuples. For example, this area and perimeter of a rectangle function has two output area and perimeter. Just assign them to a variable. You got a tuple of elements. I'm providing a variable tuple two and assign the output of the function with some input value. Print the tuple two and you will discover the data in the form of tuple. If you want to confirm, check the data type of the variable. If the elements in the tuple are sad that they need to be recognized with the help of the tuple and they do not have any individual identity, it is possible to give separate name for the element in the tuple. If you have individual name to the elements of the tuple, you can assign them if you need to recognize them separately. The element have got individual name and they are happy. Tuples can be used along with and inside the list. Here is the list of tuples with name and age of few uncles and aunties. I have a disclaimer like ATVsu. I don't have any idea about your family members or friends who have same name or age. These are random names I have taken. If you found any similarities, it is just coincidence. I hope it is clear. You can access the details of tupels using for loop. Each loop has two elements, name and H, hence taking same variables. For name comma H in list of uncles and aunties, I want to print the statement in the format of particular person is so and so year old, execute the code. Just like the list comprehension, there is tuple comprehension also. Syntax method, everything remains same. Here are a few examples of tuple comprehension. Not explaining what are the elements of each of these tuples as you have become an expert now. You need to tell the Python that this is a tuple and use parenthesis. The content inside is same as that of list. Print both the tuples you just created. Hope you are now very clear with the difference and application of list and tuple. We shall see one more data structure dictionary in the next session. 32. Dictionary: A We know that list is the collection of unmarried elements. When each of the elements in the list has a partner, it will become the collection of couples, which is called dictionaries. But why the elements demand for a pair? Why can't they be single? Consider this example. In the school where you study or the organization where you work. There may be multiple persons with the same name as yours. Your name and surname are not your copyright, right? Consider in the broader terms like in state or in the country. Name cannot be used as the reference to get the information about any person in the database. So what could be the unique identification that defines only you? People have unique code like roll number or employment ID or citizen ID that differentiate the person from others. The unique element that differentiates the data from others are called key or index. Let's come back to our mapping data type, the dictionary. Dictionary is the cousin of list, like list in many aspects, but one major difference. In list, we define the elements with the help of its position. If you did not understand, we will map the element with the help of index of that element. But in dictionary, value is defined with the help of key. I know these words sound very terrible, but what they mean is simple. Just consider the dictionary that we use to find the meaning of any word. It has collection of thousands of words. How you refer to any data in dictionary, dictionary data consist of pairs of words and its synonyms or definitions. You search for the particular word, which is the keyword to get the meaning, which is the value. Similarly, dictionary is the collection of key and value pair. Let's take the same previous example of role number and names. Being a lazy man, it is difficult to find new names, so I will fetch the name I have used in the previous session. Now uncles and aunties has become college going kids and has role number. Here names are recognized with the help of unique key, that is role number. Keys cannot have duplicate, but values can be. We define the value with the help of key unlike list in which element is defined by index. You can even use function get like list, dictionaries are mutable. You can add, modify or delete the elements in the dictionary. Say students are exchanged between the university. Now Smith is replaced with Mike for the row number one not three. Update the role number one or three with Mike. Now print people. If you feel lazy to write update, just as a new value to that keyword, your work is done. Dictionary name dot keys as well as dot values, as their names suggest, return only keys and values of that dictionary. For the dictionary, people, people dot keys, return all the keys in the dictionary, and similarly People dot values return all the name of the people. Dictionary is open for all. Adding new member to the dictionary is easier than adding jam or bread. Assign the new value to the new key, you are done. Being the brother of list, mutating the dictionary is more or similar to that of list. Like list, you can remove or pop the elements. Consider one more different example of using dictionary. Here I am defining the properties of the car. Using this way, dictionary can be used to store the information, access the data, and add more information. Genius Iu might have observed one thing in dictionary. Syntax for assigning the values to the key or for learn one get on free. Same method is used to adding new member to the new key and also updating or replacing the old values with a new to the existing key. Syntax remains same. Just include key in square bracket and assign the element. That's it. Same method can be used to alter the elements too, just as a new value to the existing key. It will replace the old element with a new one. Most list operations hold good for the dictionary like adding two dictionary and pop. But instead of index, you ski. That's the only thing you need to remember while dealing with the dictionaries. I don't want to make you sleep. Try to practice the dictionary concepts well and we shall meet in the next module. 33. Introduction to Libraries: What is a library? This is not English class. We have nothing to do with its definition, so let us not worry about it. What comes to our mind when we say library? As per our understanding, library is the collection of useful resources like books or articles that are stored in one place so that we can access any resources when we need. Similarly, in programming, we use the treasure full of pre coded resources to make our programming task easy, which is called libraries. It's just like when it is difficult to prepare pizza, order plain pizza from the nearest seller and customize as per your requirement. As we discussed in the beginning, one of the reasons behind the Python popularity is the number of libraries it offers. We can count the muscles or nerves in our body, but we do not have the count of libraries in Python as they are increasing day by day. But wait. Now you have become the expert in programming. Then why you need libraries? It is very important to learn the libraries because we do not use the programs just for computing basic calculations, but to solve the complex task like developing software or programming difficult problems of science and engineering, for example, machine learning. Technical problems like these are difficult to program if not impossible. It is necessary to write heavy program even for minor details of the problem, but are we the only person who work on that category of problem? Definitely not. We are not the first person and not even the last one. Problem statement might be different, but similar algorithms were used by many people. Hence the commonly used algorithms were pre coded and stored in the form of library. We can use the resources from the library to complete our task. In this module, we talk about the unsung heroes of programming, the libraries, like the backstage crew, who might not be visible for the audience, but without their effort, end result might not remain same. I have already given a lot of buildup for the libraries. Now we'll introduce a few of them. Here is a list of popular Python libraries. You can pause and look as I cannot stand here. As we cannot discuss all of these libraries here, let us explore two popular and commonly used Python libraries. Math and Numpi library as example. Are you excited? Give me thumbs up and join the next session. 34. Math Library: In this session, we explore the math library. The name of this library reduced my effort of defining the library. It does what it says. In simplest term, it is the mathematical library. To use the library in US system, it is necessary to have them installed. To install any library, type PIP, pip install library name, here I mentioned math in the console. Wait for the packages to get installed. Installation is done. Library is ready to serve your programming need. Let us start with simple use of math library as you are a beginner and I cannot make you to learn to drive the truck directly. Let us start with a bicycle using the math constants. Bicycle has two wheels which are circular in shape. Let us go back to the problem of calculating the area of the circle. For calculating the area, we use 3.14 as the value of Pi. Anybody here, genius enough to define the value of Pi precisely? Even if you know the most precise value, do you have that much time to write the decimal values? I don't think so. Why we even worry about it when the math library can help us? Math library define the value of Pi to the best possible precision. First step, we need to call the Math Library for help. Ladies and gentlemen, please welcome the math library to the work. No, math library will not appear if we call like this. This is not the way to call the library to bring the math library for action, write import math. This will get the math to work. Now math library is ready to help us. Now I replace the value of Pi with math, the library name, which alert the math that we need some help. Then dot Pi, which inform math that we need the value of Pi here. We can see the value of Pi is defined by math. This will work fine, but calling the whole library just for one or two function is like calling the whole army to fight with one person. In such case, call the math to give us access only to Pi. From math, import Pi. If you need more than one, but still very few functions, import them using comma, like in this example. Remember, sine take the argument in radiance, not degree. Hence, if you have angle in degree for the technometric problems, convert them to radiance first before you feed them to the calculations. If you have more functions, then it is better to call the whole math library. Are you facing difficulty to convert them from degree to radiance? Why you worry about conversion when we have the math library? You can convert the angle in degree to radiance by using function math dot radiance. To get the angle back from radiance to degree, we have the function math dot degrees. Along with Pi, math defines a few other mathematical constants like E and tau. Math will bring mathematics to your programming. Now let us move to trignometry. I know some of you might have started feeling sleepy hearing the name, but don't worry. I'm not your math teacher. I assume you have attended your math less promptly, and you know sine, cosine, and tangent well. We just see how to use them in math library. First, sine function. I do not measure the sin, but measure the sine of the angle. Angle we have assumed is Pi divided by 4 radians, which is 45 degree. Similarly, math dot cos function, measure the cosine and math dot ten return tangent of the angle. Everything here is easily understandable. Just add A in front of them. I mean, A sine A cause and a ten, they get converted to inverse sine cause ten respectively. Add H at the end of them, sine h, cse H, and tan H, they become hyperbolic. So easy to use math library, right? Now comes exponential and logarithmic functions to the math party. EXP, which stands for exponential of X is constant E rises to the power of X. In the current example, E is rise to the power of six, which is approximately four not three. Next function is log. Log need two assistance in the form of arguments, value and base. First example, logarithm of 81 base three. This gives riddle to the math, three to the power of what is equal to 81. According to Python math, it is four. If you have any objection, clear it with Python. Pow is power with two arguments. Power gives the power to rise the value exponentially. Power of X comma Y indicate X rise it to the power of Y. In this example, six is raise it to the power of four. SQRT stands for square root, square root of 625 and 156.25. Now let us see a few numeric operations of math. Here you see permutation and combination of N and K in the form of N permutation K and N combination K, where K is less than or equal to N. Otherwise, you get error. See another popular math function, GCD, not the brother of LCD. It means greatest common divisor of two integers. The room you are sitting now has ceiling and floor. Ceiling is the nearest upper surface of the room, and floor is the lower surface of the room. I'm not interior designer of your room. I'm talking about them because math offers SL and floor to the numeric values. Math dot C is nearest higher integer of the argument X, and floor is nearest smaller integer of argument X. There are other functions like Fabs, where F keeps the value float and ABS is the nickname of absolute the function factorial explains its purpose. There are more things math can do, but I don't want to make your head a room of confusion. These functions are most widely used, and if you want to dig more, ask anytime anywhere teacher, Google or refer the math documentation. It offers detailed information on the math library or any library for that matter. Search for math documentation in Google. You will find it. Now we shall explore one more popular library, NumPi but after a small break. 35. Numpy Library: Okay, everyone, please gather around. We are now going to learn about one more Python library, Num Pi, which is a nickname for numerical Python. Get ready for the adventure with Numbi. But who is this Numbi? We need some introduction of our chief guest. NumPi deals with multidimensional array and matrix data structure. When you think of scientific and engineering problems, then think of Numpi. Numpi allows a lot of operations. It's fast and efficient. Numpi would be something you cannot afford to miss if you are a data science or machine learning enthusiast. To install Numpi as usual, the same statement PIP install Numpi or Conda install NumPi if you're using anaconda. I have already installed Numpi Hence in sweet words, it's telling what happened to you? The package is already installed. Once you install, call it for work using the statement import Numpi and ask its portion with itself. Use to underscore on both side of version. Already in math library, you might have observed that when we work with the library, we need to call its name frequently to use their functions. It is difficult to call it again and again with its full name, as we humans are very lazy. NumPi is already the short form of numerical Python and we keep short name to a short name numpi say NP, which is very popular nickname to it. Okay, lazy guys. Now let us create an array. I call NP for help and say, I need to create an array and enter the elements. Creating array with the NumPi is so simple. Even the list can be converted into array. Here, the list is defined and same elements are provided to array. Why we do that when we can keep it in the list format? Because NumPi array is very strong and powerful than the list. It can handle heavy lifting and accommodate complex matrix operations that list cannot even imagine and make R if you ask the list to do so. Rnm dot D type will return the data types of the elements in the array. If you need to alter the datatype of the elements, add the statement of T type and define the required datatype while defining the array in this format. The number 64 indicates the number of bits per element. This is commonly used in C or Fotron. For most cases, use end 32 and float 64 for good accuracy and speed. Tell you the numpi is multidimensional. If you said no, then you must be feeling sleepy. Please wake up. Here is an example of two dimensional array. Two dimensional array is a matrix that we use in mathematics. Array shape will return the size of the array. It means two rows four columns. Np zeros will create the array of zeros. Zeros with just one argument make one dimensional array. In this case of five zeros. Similarly, two dimensional zero array with rows and columns can also be defined. One step ahead of this is the example of three dimensional array. Here is how it looks. Like us, NumPi cannot go beyond the third dimension. In a similar way, we can create the matrix of ones, which is filled with the value one, and I for identity matrix. But identity matrix take one argument because it is symmetric and must have same number of rows and columns. In other words, identity matrix is a square matrix. I assume you have went to your math class in high school promptly and learned the matrix operation well, as I cannot teach you the mathematics now. We just look at how to perform the operations in Numbi. Array dot T is the transpose of the matrix which does magic and convert the rows into the columns and columns into rows. I will create one more matrix for the operations, array seven, which is also two cross four matrix. Now I'm adding array five and array seven. Adding two or more matrix is as easy as adding numbers. Only condition for the addition and subtraction of two matrix is that the size of the matrix must be same. Otherwise, you don't get the output but error instead. Multiplying the matrix with a constant will multiply the value to each element of the matrix. In Num Pi, finding the inverse exponentials and root of the matrix are very similar to how we do that to a constant value. Now look at the operation that broke your head during your schools matrix multiplication. Very simple, but the number of columns in the first matrix must be same as the number of rows in the second matrix. It is not the rule of num Pi, but the rule of mathematics. Your headache is solved in a matter of seconds. Now create the array based on arranging the values. The function arrange is the brother of range that we use in four loops. It works same as range, first value, last value, and step size. But what it does is it creates one dimensional array. If you want to convert any one dimensional array into two dimensional array, use the method reshape. Reshape will break the long chain and provide new shape to the array. Now let's meet our old friend slicing. Slicing one d array is exactly same as we slice in the list. Here, let us go one step forward. Two dimensional slicing sounds complicated, but it is not. It is as easy as one dimensional slicing. Here we treat the row number and column number as index, but start the count from zero. Two dimensional slicing will return the sub matrix from the matrix. Here is the example of how the two D slicing works. Consider only row first. You know well that zero colon two is zero and one, one step less than two. I have selected zero through two first row. Now consider column. As per the index for one column four, select column one, two, and three. Now the coinciding matrix is our required result. Is it really difficult? I don't think so. When we need to practice the concept of programming, but we don't have the real data, what we should do? What is there to do? Create random dummidata to work with. What if I tell you, Numpi can do even that for you? You can create the random array by defining the size of the array and range of values you need. I will create the random list of integers using random dot Randent. Random is the function in Numpi and randint is sub function in random, which written only integers. Are you okay with anything from zero to infinity? No, then provide input range, S numbers within 50. Followed by the size of the array, I need five cross five matrix. I will create a three by five matrix of fractions using random dot rand with size of the matrix. Great. Now I strictly say the Python, choose the values only among the provided list, which has five elements. Obviously, method name is choice. The rest of the process remains the same, give the size of the matrix, for example, three cross three. Now let us extract the value from the array based on some conditions. First, I will create the random array of integers within ten and size 12 and assign them to a variable named data. Now extract the values based on some conditions like elements greater than three in data. Extract the numbers that are divisible by two or simply even numbers. Great. Now we shall explore one more method, empty array, but it looks like the zero array. What's the difference? Difference is elements here are uninitialized that cannot be used for any operations, but you can add the elements using other methods like using four loop. Enjoy the libraries. Math and Numbi are popularly used library of Python, hence we have selected them. But Python supports thousands of libraries serving different purpose problems and fields. We shall end the module now. You can learn the other libraries as per your requirement. We shall meet in the next module. 36. Pandas: Hey, there. Before exploring machine learning algorithms and data science projects, it is important to learn a few libraries that are very much needed for programming. As part of that, we shall learn about Pandas today. Yes, I know what you are thinking. Pandas. Are we here to watch cute Panda videos? I wish, but Today we are talking about the Pandas library in Python, and trust me, it is equally adorable, but in a programming way. For anyone dealing with the data, Pandas library is as lovely as the animal. Let's start Pandas with a little story. Imagine you are in a massive never ending supermarket called Data Mart. All around you, there are rows and rows of data. You witness huge amounts of data everywhere around you, mostly unorganized. You are there standing clueless, holding a tiny shopping basket, wondering, how on earth do I find what I need in this mess? Well, my friends, that is where our superhero comes in Pandas. He helped you find what you need among the infinite rows of data. So Pandas is a powerful data analysis and manipulation tools. For Python, that will help you find, clean, organize, and manipulate the data like a P. You could say Pandas is like that one friend who cleans up your room and then help you find your lost things if your lost items were actually a data. Okay, forget that. Here is the real deal. Pandas gives you two magic tools, series and data frame. Think of series as a single column like a shopping list, and data frame is the entire grocery cart, a table that can hold multiple columns of data. So basically, a series is a column, and a data frame is a collection of those columns. Want to slice and dice your data like a chef. Pandas has you covered. Need to find all the people named John who bought bananas on a Tuesday. Pandas can do that, and it won't ask why you need to know. Imagine asking your friend, Hey, can you find all the people named John who bought bananas on a Tuesday? They would probably look at you like you have lost your mind. But Pandas Pandas will do it without judgment because it's a library and libraries are cool like that. Now let's create a series and data frame because talking theory is like watching a cooking show and never tasting the food. I'm not here for that kind of torture. Here is how we do it in Python. Folks first import pandas, import pandas as PD. Pandas, of course, is too cool to use its full name. So we just call it PD like we're best buddies. Let me create a series of number of fruits at a store. Number of fruits is equal to PD dot. We are calling our best per D pandas and ask for a series. 152230 are number of different fruits. Print number of fruits. We have defined a series. You can observe one more column appeared with 01 and two. This is the index, unique reference for each of the values in a series or in the data frame, just like we had index in the string or list. The index in a Panda series is like a name tag. It tells each value who it is. You can even rename them. Let us make changes while defining itself. A index is equal to list of apple, banana, and cherry. Printing it again. Now our series has become something meaningful. Want to have more fun, I will rename the existing index with a new list of index using number of fruits, our series name dot index is list of fruit images. If you're using Windows, use Windows key plus semicolon and in Mac, use Control plus Command plus space to open Images picker. I will add images of different fruits. Print series again. Now your series is fruity and fun. Now let's create a data frame. Name of data frame is DF, name whatever you want. Dataframe must have multiple columns and each column must have a column name. Our data frame has three columns, name, age, and favorite food. Each column has four rows of data. Names we have are John, Jane, Jake, and Jill. All have names starting with J. What a coincidence. Data we have in age and favorite food, are these people's age and food they like respectively in the order. Let us print this data frame so that you get a better idea. We have got ourselves a data frame. John is 28-years-old and like pizza and so on. Information is printed in the tabular form. Okay, now that we have cocoed up this tasty data frame, let us learn how to slice and dice it like a professional chef. But no crying over like slicing on in here, only joy from data slicing. Want to grab a specific column, es DF with only name, and we get a series of names, just like you had to call out role in a classroom. In the real world, data isn't as tiny and neat as four rows of hand typed information. It's a wild jungle of thousands and sometimes millions of rows. Imagine sitting down to manually type every sales transactions, every customer details, and every inventory update, your keyboard would probably pack its bag and live forever. Thankfully companies are smarter than that. They maintain all this data in handy spreadsheets, Excel files or CSVs. It is like having a treasure full of information, neatly organized and ready to use. Instead of wasting time manually creating the data frames, we just import the file in Pandas and boom, your data frame is ready in seconds, let the spreadsheets do the heavy lifting while you focus on digging into the insides. So now we read CSV file with Pandas. I'm using employee salary data. It is a Dummi data with 50 data points. Import the data using pd dot, Read CSV, and then path to the file. You need to specify the location and directory where the data is stored. I have stored the data in the homepage of Jupiter and hence import it directly. Just like that, we have got a data frame without the hassle of defining all those loads of data, and now you are ready to slice and dice your data however you like. If you want to look first, few rows of the data frame, check dfdt head. You get first five rows of the data, and if you want to see more than five data points, just mention it. Python is very friendly. It returns whatever you ask for. Now some of you might be wondering, why should I use Pandas when I have got my trusty Excel to do all these jobs? Pandas can handle data so large that makes Excel wet. It is fast, it is flexible, and it can merge, filter, and group your data like it's a magic went. Excel is like a bicycle with training wheels, while Pandas is rocket ship that can take you to the data moon. No, I'm not exaggerating much. Next up, let's talk about set index. We had the employee data. They have unique reference, employee ID. Instead of recognized by the index like 012, they deserve to be recognized by their employee ID because it is unique. Right now, our data frame rows are indexed by these boring default numbers, but we can change that. Let's make it more personal using set index to set a more meaningful index like their employee ID. DF is equal to df dot set index employee ID. No more generic numbers. Now you can refer the data by the person's ID directly. We have data frame now. We need to extract the information from the data frames. We have two data ninjas for doing that. Lock and iloc. These are your go to weapons for grabbing specific rows and columns. But let me tell you, they have very different personalities. IloC is index based and lock is label based. Iloc is I don't care about names. Just give me the numbers guy, and that's the difference between lock and iloc. Labels versus positions. Both ninjas, both awesome. I will tell you one fun fact. Even the experienced data professionals sometimes get confused which one to use. That is very normal. Let us see some operations, then you will understand better. Starting with iloc, ILC doesn't care about names. No, this guy is all about positions. You ask for information in any rows or column, and he does it without asking questions. IoC reads row first followed by column. Now let's say you're interested in a single row, like you are gossiping about only one person in the group. You can use ILC to get that gossip. I stands for index and lock for location. Want to know about the person sitting in row one, that's how you get them. IC one, return the data in the index one, gossip successfully. But remember, iloc is all about position. Like in sequenced data types, colon is used to mention the range. This line is telling to return all rows and column one. Column one is not first column because we have zeroth column. I hope you remember Python had a bad math teacher who taught counting from zero. Here is the output. You can display the range of rows and columns. I lock with colon three comma zero, return rows zero, one, two, and column zero. Next, we have Lock. This guy is all about labels. He says, give me a name and I will find the data for you. He's precise, focused, and doesn't care about the position. You can use him to grab the specific rows and columns by their labels. I want to know the name of the person having employee ID e003. Only name. Let me ask dataframe dot log row e003, column name. Okay, I don't get any other information just with the name. Who stopped us from getting more information? Just write df dot log e003. There we have it. That employees entire life story right there. Let us give some twist. Get data based on some conditions, dataframe dot log, find data of all person having their salary greater than or equal to 3,000 units. We are interested in only those who make good money. These are those people. I'm also concerned about their departments. I want to find those people having salary 3,000 units and belong to IT department only. These are our short list. In any datasets, there are good amount of junks along with the information. Lock help us in filtering the data and servers that only we are interested in. Thanks, Log. Now let's move to some fun methods. First up, the describe method, the data analyst version of reading someone's entire life story, but less dramatic. So df dot describe Describe gives you all the juicy statistics about the data frame. It is like data's resume, the mean, the minimum, the maximum, everything you need to make judgments. Now let's calculate something simple like the mean edge. I mean, why not? Df h dot mean. That returns average age of our data friends. That means statistically speaking, our group is pretty young and energetic. Let's talk about uniqueness. The unique function will tell you all the distinct values in a column, like pointing out all the unique personalities at a party. If you check for unique values in department, you get list of the departments used in the data. All data belong to one among these categories. Let us filter some data now, like you're filtering your Instagram feed to see only what you really care about. This works same as the lock method. For the previous data frame, suppose we want to find all the people whose favorite food is pizza. Easy. DF having DF or favorite food is equal to pizza. Now let's talk about merge. This method is like a matchmaker at a party. Its job is to bring different datasets together like finding two long lost friends. Suppose you have two data frames, one with names and ages and another with names and cities. If you see names, they are same. That means there are two data frames belong to same people. Naturally you want to combine them. Who is ready to manage two datasets belong to the same people. That is where merge steps into the play. Create a new data frame, merged df is equal to pd dot merge, DF one and DF two. Based on what should I merge? We need to merge on comparing names because names are same. That displays the merged DF like that, the names, ages and cities are all living happily ever after in one data frame. Merge is the master of matchmaking, bringing data together on common ground. In this case, the name column. Next we have join. Now join is like merge, but it works more like neighbors sharing offense. It joins two data frames side by side based on their index. Suppose we have set the index of both data frames to name. Now join them based on name. Join df is equal to DF one dot join df two. See, neighbors living side by side, sharing all their secrets in one nice joint dataframe. Now let's say you have got two datasets and you want to stack them together. Either one on the top of the other or side by side, like building a data sandwich. Enter Concat. Here is how you can stack two data frames on top of each other like you're piling up pancakes, pd dot Concat df df two. But if you prefer side by side actions, just change the axis, pd dot Concat df df two. Acess is equal to one. Concat lets you build your data skyscraper anyway you like. Now let's check the type of data in your data frame. This is asking, what are we really dealing with here? Is the He column full of integers? Is the city column full of strings? Let's find out df D types. We have got integers for H and subjects, a fancy word for text for city. Now we know exactly what kind of data we are working with. Now, let's say you want to change someone. I mean, change the type of a column. Maybe you have decided that the He column should be a float instead of an integer. Es PC, and done using astype. Tfh is equal to dfht astype float. He is now a float like a number that's ready for some serious math. If your data ever needs a makeover, astype is your tool. And that my friends is your Pandas tool kit. You have got set index to personalize your data, lock and ei lock to grab specific slices, merge and join to bring datasets together, and concat to stack them like data sandwiches. Now go out there and make some data magic happen. And remember, when you handle tabular data in Python, Pandas is something you cannot miss. Now you must be feeling Pandas as cute as Panda, the animal or horrible like angry Panda. With practice, even angry panda, turn out to be cute one, see you in the next class. 37. Matplotlib: Hello future data artist. I will tell you one hard fact. Most of us are allergic to numbers. Working with huge numeric dataset is the best way to fall asleep in minutes, even better than sleeping pills. Today we are learning visualization and with visualization, we are turning the boring numbers into colorful stories. Yes, that's right. We're about to become data artist. Welcome to the world of Matplotlib, the library that lets you create beautiful graphs and chart from your data. Because numbers without visuals are like pizza without toppings, boring. First thing first, what exactly is Matplotlib? It is your personal canvas for drawing charts, graphs and plots from your data. Imagine your data as a giant pizza. You have got all toppings, but matplotlib is what lets you slice it, present it, and make it look delicious. All right. Step one, importing Matplotlib, setting the stage. Let's go to the code. First, you will need to import Matplotlib. Instead of typing out Matplotlib every time, it's your full legal name, we call it PLT because we are cool like that. Import matplotlib dot Piplot as PLT. Now we are ready to roll. Let's start simple like a baby's first step, but without filing. Suppose you want to plot how much coffee you drink every day. So days is equal to Monday to Friday. We are considering only weekday because on weekends we don't drink coffee, we drink something else. Coffee cups is equal to two, three, one, four and two. PLT dot plot. Das coffee cups, plt dot show to display the plot. Here is your first plot. What does it show that you have an inconsistent caffein habit and should probably see a doctor by Thursday? Now this plot is nice, but it feels a bit nameless. Let's give it some labels and a title so people know what they're looking at. Because without a title, it is just a bunch of random lines. First, let's name Xs, plt dot X label, days of the week. Now YXsPLt dot Y label, cups of coffee. Finally, a good title to the plot. Plt dot title, caffeine consumption, now plt dot SO much better. Now we know this is a story about your caffeinated journey through the week. Now let's add some color and style. Sure the plot works, but it's plain like a toast without butter. Let's spice it up. You can change the line color and style to make it more visually appealing or just to flex your artistic flare. PLT dot plot, Ds oma coffee cups, color equal to red, line style equal to dotted, and marker is equal to O. I will keep other things unchanged. See what happened now. Can you spot changes? Check it out. Now we have got style, red line, dashed pattern, and circles on each point. Like we're throwing a disco party for your coffee addiction. Let's take things up a notch with a bar chart because sometimes line charts are like spaghetti, too wingly bars they're solid, confident, and stand tall. Here is how you create bar chart showing how much pizza you have eaten this week. Days remain same Monday to Friday. Pizza slices is equal to four, three, five, two and four. Plt dot bar Des pizza slices, and I will label X label as days of the week and Y label as pizza slices, plt dot title, weekly Pizza consumption, finally plt.co. Boom. Solid bars representing your pizza consumption. Not only do you love pizza, but now the world knows about it in glorious bar chart form. And remember, no one is judging your wetness taste binge eating. Next up, we have got pie charts. They're great when you want to divide things into neat little slices. Plus you can always pretend it's actual pie. Let's say you want to visualize the different type of foods you have eaten this week. So foods equal to pizza, burger, sushi, and pasta. Amounts is equal to 35, 25, 15 and 25. PLT Pie amounts, ma labels is equal to foods. Autopicity is equal to one decimal points. PLT title, food breakdown for the week PLT dot SHOW and there it is a pie chart. Look at all those delicious slices. You have got 35% pizza, 25% burgers, and probably too little sushi for your own good. Just like a real pie, this one makes you hungry, isn't it? Subplots, multitasking like appro. Now, what if you want to show multiple plots at the same time, subplots to the rescue. Think of them as the Netflix screen with all the different shows. Only instead of binge watching, you are binge plotting. Let's make a subplot with a line chart and a bar chart side by side. First subplot, PLT dot subplot, 12 comma one. This means layout has one row, two columns, and this is first plot. PLT dot plot, Des coffee cups, PLT dot title, cups of coffee. Now second subplot, PLT dot subplot, one comma two comma two. This tells second plot. This time we have bar, plt dot bar, Das coma pizza slices, plt dot title, pizza slices, plt dot tteyout plt dot sh. Now you can look at your coffee and pizza habits simultaneously. It is like multitasking for your data brain. Plus, it is a reminder that your food choices are just as important as your caffeine addiction. Egends the side kicks of every hero plot. Think of legends as information board. We shall have the plot of coffee cups and pizza slices in same plot PLT dot plot. Das coffee cups, label is equal to coffee, PLT dot plot. Das pizza slices, label is equal to pizza. Plt dot X label, days of the week, plt dot label, quantity, plt dot title, Coffee versus Pizza consumption. Now you need a legend to tell people what is what, or else it's just a bunch of confusing lines, plt legend and PLT dot Show. Now we have got both coffee and pizza consumption in the same plot with a legend. It's like an epic battle Coffee versus Pizza. Who will win? My money is on pizza. What about yours? Customizing the plot, adding grids and tweaks. Feeling fancy, let's add a grid. It's like putting lines on the map. It helps you navigate through your data. I will add one more line before PLT show plt dot GRID. True. Now it is like playing battleship, but with your coffee and pizza data. It makes everything look more organized and let's be real, a bit more professional, saving your plot for future reference. Finally, you have made an amazing plot and want to save it. Maybe to print it out, hang it on your wall, or show off to your data scientist friend. Easy plt dot Save fIC and your image name myplot dot png. Now your plot is saved as an image forever immortalized in your data journey. Frame it, gift it, or just tear at it proudly. That, my friends, is matplotlib in its glory. You have learned how to create line plots, bar charts, pie charts, subplots, and even how to save your creations for future generations. You're officially a data artist now. Go forth, create beautiful visuals. Happy plotting. 38. Introduction to OOP: Welcome to the first lesson on the last module of the course. The concepts you have learned till now are like your well known friends and relatives. You know them already and meet them regularly. Operators, logic conditions like and or not, decision based on comparison, loop like routine works, collection of data, everything you use in your day to day life, even before knowing what is a program, and you might not use those fancy terms. We have just introduced their programming versions. You have learned how to use the same things in your program. Those concepts made Python a good scripting or functional programming language. I know you hit that difficult to digest big words, but their meanings are not as complicated as they sound. It means programs were mainly based on logic and some action. Let's go through another unseen phase of Python as object oriented programming language. I know this term create panic among the listeners, so let's call it OOP. If you're very courageous, go to any search engine and find what is OOP. You will feel it like the plot of horror movie. In fact, there is no such complexity in this concept. Even OP is something you know already. But the problem is the complex and scary definitions make it feel like OP is brought to Earth by aliens. The fact is you have met them without knowing about them. Hence Pi may seem a bit confusing at the beginning, but don't worry. I will try my best to keep things as simple as possible. That's my promise, and you must keep your promise to practice as much as possible. This model might be a bit lengthy compared to others, but we shall have more fun in this module. Show me some enthusiasm, guys. You are learning something new and learning should always be exciting. Forget about programming now. What do you understand by the term object oriented? We are trained to find complex things even in simple words, don't use much brain, only use fraction of them. At least you will understand that this is something based on objects. When you started learning English, I think object is one of the word you have learned within a few days. You know this word very well so that you can explain better than me. Then what is an object? I don't want definition, even I'm scared of it. Just by using ordinary common sense, can I say everything your wide open eyes can see when you look around are objects. As you're watching this video, there must be digital gadget, maybe a laptop or smartphone or a tab. That gadget might be resting on a table. I can see a lot of objects messed around my table. That is one of the indication that I am an engineer. That table, laptop, WiFi router, pen, paper, thousands of wires running long and wide, spiller food, sleeping kitty, everything, whether you kept organized or messy, are objects. This is just about the table. What if you look around the room? No, we don't have that much time to list everything. Let's stop it if you have understood what is an object. If object is so simple to understand, then how it is possible that object oriented programming is complex. OP is a programming concept that allows us to define the real world objects and their properties. If you understand, then great. No doubt you are very intelligent. If you don't, you will understand as we proceed. OP is the hidden talent of Python, but it is very important to learn to be a good Python programmer. As a programmer, you get a lot of powers with OB. Keep your first step ahead towards Op. To understand OP, it is important to know the terms user. Imagine entering kitchen without knowing the kitchen ingredients. You may end up with good science experiment rather than dinner and God bless those who are supposed to eat it. Let us understand OP terms with an example. Do you like fruits? Don't worry much guys. Even if you like it or not, I don't make you to eat. If you're feeling hungry, I'm extremely sorry. You can pause, get something to eat, and then continue. Fruit is the real world object. We need to define the fruits in the program. Assume I'm computer and someone explain me how a fruit look like, and you don't need to explain me in Python language. You can use the language you understand, and of course, the language even I understand. Is there anyone who can answer this question? This question is very general and someone may ask which fruit you are talking about. If someone ask how to recognize mango, I can answer yellow color, yellow pulp, one seed inside, sweet taste. What should I answer for? How to recognize fruit? Do I need to say fruit look like mango, apple orange pineapple and so on? Where should I stop? The problem is fruit is not a single object, but it is a name for a group of delicious plant made edible objects. When I said fruits, there are hundreds of fruits available. VOP term, fruit is a class. Group of objects are called class and members belong to this class like apple, orange, mango, banana, or whatever it may be, are all called instances. In VOP, we define these instances and how to recognize them. Our aim is not to send the computer to market to get some fruits, but to store the information on how to recognize and differentiate each fruit. How to define each instance of fruit class. Distinct property of each fruit comes for our help. Each instance of fruits are identified by set of distinct properties like color, odor, taste, with seeds or not. If the number of seeds, where to throw those seeds or other properties which help us to recognize among the list of fruits. These properties which define and differentiate various instances of a are called attributes. Attributes help us to recognize the person you are meeting for the first time. Skin color, hair color, and maybe height can be among the attributes of a person, but don't define his or her dress color as attribute. OP is innocent. It may take any input from you, but you don't know diss color can change tomorrow. Hence, attribute must be universal property, help to recognize the instance. Now we got an instance of a fruit, and with the help of attributes, we have recognized it as an apple. Next question is, what do you want to do with that instance? That's my personal choice. Depending on the requirement, I may directly eat it after slicing, or I can extract juice from it. Any operations performed on the instance are called methods. Do you remember method? Let's discuss about method in detail soon. Are you clear with the terms class instances, attributes and method? These words may be new and strange, but their meanings are very simple. We know these concepts very well, but you just don't call them as classes, instances and all. That's it. These terms are very important in every concepts of Python programming. In fact, we have encountered this term multiple times while programming. It just worked like secret agent, hence we could not recognize it. Now let's recognize. I will define my as usual string. This is a string and assign this string to a variable named string. Don't get confused. When I ask the Python to print the type of this value, look how the output is presented. It's not saying data type string. Instead, it written class Star. You know Sterr. This is how string is called at its home. Does this keyword class STR says? It says the value you're talking about is an instance or member of the class string. That means class is not stranger. Class was with us since datatype module, but he was not communicating with us. Might be introvert. Similarly, if you ask Python, what type of value is two? Python says he belongs to class It. Not just string, but all the tring in float complex list dictionary. What we used to call as datatypes are all classes and value belongs to these data types are instances of these classes. Type function, which we thought earlier to return the data type is actually a built in function that returns which class any object belongs to. Then what about user defined function? His function is from Mars or any other distant planet, then it must be no different. Let's check it, however. Why should we keep doubt on? As you know it very well, how to define a function, I will define a simple function without any parameter. Say, define message which prints some message hello world. This is a dish without any ingredient. Yes, it is possible to define a dish without ingredient. Not in kitchen, but only in Python functions. But such function will always return same output. There is no change in the life of this function. How boring isn't it? Okay, let's come back. If we ask which class do this message belongs to, you will see class function. That confirms function is not from MRs. It is also a class and defined functions are the instances of the class. Everything we define while programming belongs to some class and each class has their own set of attributes and methods. Dot notations we use on data are the methods we are operating on the class. That answers the old question left unanswered. When we use Inumeric on the integer value, we have encountered the attribute error with the message int object has no attribute is numeric. The terms used to be scary then must made sense now. It was actually saying, I am instance of in class. I don't have any method called is numeric. I hope it's clear. Now we have understood each data being instance of a class have the methods of its own, but we are not the storage device to remember the methods of each classes. How good it will be if you find the list of all the available methods for any given instance. Python is so sweet that it understand and provide us what we need before we ask for it. DIR function with a instance as argument, return the list of the methods available for given instance. Will use DIR with string, but the problem is output feel like alien language rather than Python. For a moment, ignore those sitting inside the underscore. Concentrate on the other methods. Feels like familiar faces, isn't it? The ones with the double underscores on both sides are not the users use often. They were called in the back end of the processing to perform specific operations. For example, underscore underscore a underscore underscore is called in the back end when you add two strings. These special methods are like chefs specialized in particular dish who work in kitchen. When you order Python to add two string in the service area, Servo transfer the order to the chef in the kitchen, underscore underscore, add Underscoe underscore. You don't get to see the work of chef, but the final output is served to you, concatenated strings. Similarly, underscore underscore Elian underscore underscore is another chef. He's called for work when you ask the length of the string. Works in kitchen and you are returned with a desired output. Hence you don't see these special methods in user interface, but they work silently in the back end. These special methods with double underscores on both side are called Dunder method or magic methods as they work behind the scenes. I think your fear is resolved now. Similarly, I use DR function on the list to get the list of methods available for a list. Now we don't need to remember any methods. DIR has returned the list of all methods of a class. Do the programmer is happy now? How can this be possible? Programmer being humans, our demand never ends. DIR has returned a list of methods, but is there someone who can explain how to use each of these methods? Python know about us very well. He has granted that too. Do you remember our old friend help or forgot him? Just use same help function with your instance, Python explain how to use each of the methods available. Python gives all possible help to develop the good program. If you're looking for a function that write the program, then sorry, Python don't have it. By now, you must have realized OP is core behind all concepts of Python. Even the libraries are created with the OP. For example, math is the library we have discussed in the previous chapter. Import math and ask Python what type of class is math. You see its module. Module is a special class of Python that allows user to utilize its objects by importing. You can see the list of all methods stored inside the math module using Dire function. You might be familiar with few of these methods, but some like this dist we have never met before. Tell help function that I have met a stranger in the math module. Can you please help me to get to know about this method? Help function says, relax. Distance return the Euclidean distance between two points along with the formula. Learn it if you want and it is relevant for you. If you have nothing to do with Euclidean distance, then forget it. Not just math, all Python libraries are instances of class module. That concludes the current session. I'm very sure you have felt OP easy and interesting. You have much more interesting things to learn in OOP. You have seen the built in classes of OP, but there is no much thrill in using the classes defined by the Python developers. Real adventure is defining our own classes, instances, attributes, and much more and play with it. That must sound exciting for you. In the next session, we learn to create the object classes of our own. Let's meet and explore together more interesting things in the next video. 39. Defining Objects: Welcome back. In the previous session, we have learned about fruits more than any botany class. In this model, we teach computer what we have learned. I mean defining objects. Let's not break the flow. Take our favorite example fruits because fruit is something almost everyone knows. Is there anyone who don't know about fruits? If by chance there is someone, then there is high probability that either person is new to the English language or new to this planet. Define the class fruits, just like you define function. But with the keyword class, class fruits and end the line with colon. Just telling Python, there is class of objects called fruits. We define other details like instances later for now pass the statement to continue. What is this pass? Pass is a keyword that absolutely do nothing. Strange. Why do we use something that do nothing? Sometimes we need someone who do nothing. We are alone, we feel to have someone just to spend time with us and nothing else. Pass is such a companion, use it as placeholder for future code. If there is nothing to be included in the body of a function or a loop or a class or even if statement, pass can be used to tell Python, I will provide the other details later. That is because you cannot leave the body of a function or a loop empty, pass can be used to avoid getting error. Is it clear? These lines. Now Python know there is a class of objects named fruits. Now define first instance of fruit class. That is apple. If you don't like apple, you can define mango. I have no objection. When we define an instance, first ritual you need to perform is to tell Python that this instance belonged to fruit class. Who on Earth do not know apple is a fruit? Computer don't know because it never went to market. Now Python understood, Apple is a fruit. Now we shall define the attributes of apple instance. That is property that define the particular instance. I will define two attributes, color and taste. Let me define. Apple dot color is assigned with red and apple dot taste is equal to sweet. This is like defining if you find a red fruit with sweet taste, then it is apple. I know two attributes are not sufficient to explain any instance. Once you learn OOP, you can define all the other attributes if you have time and patience. Now for the sake of learning, two instances are good enough. Similarly, I define another instance, fruit orange. The color of this fruit is orange, same as its name, and taste is sour. Have defined two instances with two attributes each for fruit class to extract any attribute of any instance, print orange dot taste. Similarly, apple dot color. You get the dessert details. Let's define a function for making the introduction of the fruit. DEF function name introduction and parameter is self. Self is very important term in OP. Self is the keyword used in OOP to represent or indicate or point the instance, whichever the fruit taken into account for this example. This function take instance name that is apple or orange for the fruit example as argument. In the body, print this fruit is curl Brass in color and curly braces in taste the format self taught color, which translates to instance taut color and self taught taste or instance taught taste. Function is defined. The request a function introduction to introduce orange. You get output. This fruit is orange in color and sour in taste. If you check for Apple, it prints this fruit is red in color and sweet in taste. This function is boring and something we know already. We need to learn something new. Are you ready to see a magic? Using the magic, I convert this function into a method, dot notation. Move the same function inside the class fruits. Important instruction is take care of indents properly. Tell me guys, do we need pass keyword now? We have left pass here because class fruits was experiencing loneliness. Now class has body, so no need of the pass. He can go home now. This magical step convert the function into method. Now introduction is not function, it's method. Run it again and write apple dot introduction and no need of any arguments inside. Self is not parameter now, but representation of instance, but it is mandatory to use self. Execute this. Output will be same as that of function. So you understood how to define a class instance, attributes and method. This is one way of defining the object class. After using the same method for a few days, we feel boring and search for new methods. So there is one more method to define the class. This is called constructor method. Name seems to be beautiful. In last two sessions, we had enough fruits. Let's stop the fruit fasting. In this example, we shall work with the integers in the class to give equal chance and opportunity to numbers. No, constructor is not biased to integers. You can try with the other datatypes too. For this example, I used my old friend rectangle. Now, you tell me what are the attributes or properties that define ctangle? Rectangle is always defined by its length and breadth or width, so they are the attributes. Let's start to construct the object class using constructor method. We define the class name with the statement class rectangle. This is the same as what we have done before. Now we need to define the attributes of the glass. For that, we use DEF underscore underscore init underscore underscore. That is saying, I'm initializing the attributes with the parameters first and very important self which indicate the instance followed by attributes name, length and width. In the body, we assign self taught length is equal to length and self taught width is equal to width. Know these lines sound bit weird, but there is a logic behind this. As we define while initializing, user provide two parameters while defining the instance. Self itself is instance, hence length and width are provided by the user as parameter or argument. Somewhere like this in the order first length and then width. We are telling Python that user while defining the instance provide you two values as parameter. That will be in the order of length and width. What you, I mean, not the Python have to do is assign the value of parameter length provided by the user into self that is attribute dot length and parameter width to self dot width. You understand, great. If you don't, then don't mess your head. I will explain when I define the instance. We are done with defining the object class and its attributes. Now I define instances named plot. In fact, multiple plots which belong to class rectangle. This is how instance is defined in constructor method. It may look bit messy, but once you understand, it is very easy. Plot one, plot two, plot three, and plot four are four instances of class rectangle. The two values they're having are the attributes in the form of parameters in the order, length and width. We have defined three parameters, but self is instance enhance pass two parameters, length and width. Now tell me, is this clear? Make sure you understand this. If yes, as I promised, let us make it clear for audience with the confusion of what the self taught length is equal to length. You can understand it now. Each rectangle is defined by two parameter ignoring self length and width. Per this definition, for instance, plot one, three is length and four is width. Agree. What these two lines mean is, we are telling Python, user has provided two values. You assign the first value, which is as per the initialization is length to self at length. Assign second value to self taught width. The value three and four provided by the user as parameters are assigned to the attributes length and width. Isn't it simple? Now we have defined four plot instances belong to class rectangle, defined by their length and width. Now I define a function to calculate the area of the plot. With one argument, I named it as ground, which is an identifier for the instance of the rectangle glass. Area is calculated by multiplying the length and width of the instance ground belonging to the rectangle. As usual, return the area. So our function is defined. Now calculate the area for all the defined plots belonging to the rectangle class. When you run it, you get the desired output. I don't want function area. Instead, create for me the method area. That's not a big deal for you now. You have learned the magic to convert the function into method. Same as we did before. Move the function inside class rectangle. But let go the identifier ground and replace it with self. When you define method, always use self to represent the instance. Nothing more to do. Magic is done. Now you're ready to give the stand up magic show. Run the code and enjoy using the method area. I will check plot one dot area. Great. As the concepts in this session can create confusion, we are going bit serious. If you have understood till now, we can switch back to one more. Let's try to learn just one easy concept before we end this session. You have mastered the art of creating functions, I don't worry much and I will create a basic function, define ad ACAB, and in the body written A plus B. Here is a simple program that add two numbers. I have created the program and you have watched it, so we know what this add function will do and how many arguments the ad function will take. But think of the user. No one will come in his dream, like we heard in the stories to explain how to use the function and what parameters it has, or even how many parameters it has. Because for the front end or user interface, program will not be visible. When we don't know how to use built in functions, help function used to come for our help like mom and explainers. We shall ask the same help function to help us with the defined function, help add. Help function will help you, but help function just written the arguments or parameters only. That is very plain meal without any salt and spices, and that is obvious. What else you expect? We have just taught Python how to cook the recipe. How in the world, poor language know what exactly we are intended to do? It is not mind reader. It is again, our responsibility to make the information from help pleasing and easily understandable. That is achieved using doc string. By now, you must have realized that complicated terms need not be having complicated meaning. In easy term, we can say providing more information. But when we use the term docstring, people will think this person has a lot of technical knowledge. Instead, if you say providing more information, seem to be normal. That's why we use complicated term for simple concepts, and doc string is something we have used already, but now making it more useful. You have learned already to comment using the triple codes. Do you remember that? Then you have nothing new to learn here. Doc string, the cool looking term is nothing but using the triple code to explain what a function does inside the function. For the example, I will add statement, this is the function that returns the sum of two numbers. Depending on your function, you can add any information. Take multiple lines if you want. I have written almost same things into lines because I have nothing more to add. Now go and check the help function again. Help function now helps very well as its name. The same concept of Dx string is used while defining classes. Add Dx string to fruit class saying fruit class define the color and taste of various fruits. Okay, now check help fruits. So it gives some information for the user. Isn't it easy and simple to understand? To conclude, doc string is the piece of text information that is left for the user of the program to explain what a function or class does and how to use it, and it can be accessed through help function. How is Opie going on for you? Is it easy or confusing? My suggestion at this point is practice creating object class with your own examples before going through the next lesson. Next session is beautiful forest. If you proceed with proper understanding, you will enjoy the serenity of the forest. If you go with the half knowledge, it is easy to feel lost in the forest. Step into the forest with proper preparation. Let's meet in the Opie forest. 40. Inheritance: Welcome to the beautiful forest of OOP concepts. You may spot wild animals here and there, but they're very friendly. You will experience variety of concepts here. After going through the two lessons in OOP, I hope creating any object has become left hand game for you now. Let me make you use your right hand tool in OOP. In this session, we learn the key concepts of OOP. They are inheritance, encapsulation, and polymorphism, beautiful terms that are capable enough to cause fear among the audience. These terms are more horrible to hear than the horror movies. But we have surpassed many such horror movies earlier. We have developed a kind of power in this lesson, we convert those horror movies into romantic movies. Are you ready? We can't fix all of them together. Let's handle them one by one. The first concept is inheritance. I hope this term is not strange one for you. Do anyone told you ever you inherit some feature from either your father or mother? Not necessarily good characteristics, I know. Sometimes we inherit bad characteristics too. What to do? We don't have any choice to choose only good features from parents and another important and exciting example of term inherit, you may be having the property inherited from your ancestors. How can you forget that? That means you know inheritance already. Are very cool guys. You make my job easy. Meaning of the word inheritance is driving the quality, characteristics, property, or asset from one's parent or ancestors. In even simple term, all good or bad things derived from the ancestors are called inheritance. That's okay. We understood the term. But what genetics and law has to do in programming? Are discussing this because even Python class has parents and children, even they deserve a good loving family. Don't worry much. Consider simple example. We have mango class and varieties of mangoes like AlfonsHydn Atkins, Neelam, are instances of mango class. The twist is mango has parent and you don't need to perform DNA test to know its parents. Class fruits that we have discussed in the previous session is the parent of mango class. Big secret here. When we think of fruits, at least few characteristics come to our mind. It's grown in trees, has pulp, seeds, outer cover, it's delicious to eat. It's loaded with nutritions and health benefits, and much more. These are the characteristics of fruits, and mango, being the child of fruit class, inherit these properties in it. Just like us, mango has some unique features too, along with the inherited features like distinct color and odor, and that differentiate mango class from its siblings. Yes, mango class has brothers and sisters too. By now, you must have understood their names. They are apple class, orange class, strawberry class, and so on. All these class inherits some properties from fruit class and have their own unique properties, and fruit class has sibling too. Maybe his name vegetable class. I don't know. I'm not their family friend. Vegetable is uncle of mango. We shall not make such complex relationships. But these fruits and vegetables inherit the attributes from class food or something else. Is there any difficulty here? Nothing. We eat fruits and vegetables daily, but we are finding unseen relationship among them. I hope it's clear for you now. You guys learn very fast. What do you eat to become so smart? Fruits and vegetables? Okay. You already understood inheritance. Now let us learn how to apply inheritance in Python. In the current example, we define class vehicle. Anyone automobile enthusiast here, you can say, yes, I don't ask you a question about it because I don't know much about it. If you don't know about it, I can talk more confidently. I have a disclaimer for automobile experts. This is for education purpose only. All vehicles, say truck, bus, motorcycle, car are individual child classes of vehicle as per the definition of inheritance. Don't ask me later, when each of these children born, it's all their personal matter. When we say vehicle class, they are defined by hundreds of attributes. I think you know it better. I define two attributes among them. DEF underscore underscore init underscore underscore self, which is attached to all classes and I define two attributes. One is fuel, defining which fuel it used to get energy, petrol, diesel, energy drink and something else that I don't know. Second attribute is transmission. If it is manual or automatic, or you can mention particularly which type of automatic transmission. Depending on your time, you can define other attributes. Let us follow the rituals of explaining the attributes that we do for all classes. It is one of the easiest thing one can do in this world. Self dot fuel is equal to fuel and self dot transmission is equal to transmission. Is there anything else easier than this? Attributes of the her class are defined. Define a method for Wehle class. When there is a vehicle, then it has to turn on to use it. Otherwise, it's just a toy or scrap, turn it on. Define start self. When user gives start command, vehicle must start. I'm not automobile engineer, so I cannot make the car switch on just by programming. I just print engine started, ready to go. You must assume engine has started and ready to go. We have defined the method for vehicle glass. Now it's time to define the child of weaker class. Even though there are tens of children to weaker class, I cannot define all of them. I define one that is car. This is the most popular child of gel. Very important step while defining child class car. Don't forget to mention its father name in the parenthesis gel. Op now knows that car is legal child of weicer class. Being the legal child, class car has a right to inherit all properties and method of weaker glass. No one can question it. When it has the legal right, class car can even take all the attribute from the weaker class. Weaker class has only two attributes and car has access for both attributes of vehicle. But if child wish to consider one, it is most welcome. But when we have option for two, why should we consider one? Define the attributes of class car, same as you do for all attributes. Define under scosce int under sconoc self, fuel and transmission which its father had along with that car has unique attributes with sunroof. With sunroof, define if the car has sunroof or not. If the car has sunroof, value is. It's I mean programmer's responsibility now to tell Python that fuel and transmission are inherited. OOP already know vehicle is parent of car sort super dot underscore underscore init underscore underscore, fuel and transmission. Now OOP understood, CR is taking both attributes from its parent vehicle class. Then what about sunroof? Sun roof is car's unique feature, so define it like other attributes. Self dot sunroof is equal to sunroof. Even though car class has inherited attributes and method from its parent, everyone has dream of having something of its own. I will define a method for car class. Not every vehicle has air conditioning. We have air condition in motorcycle, but car has define method to switch on AC, which will print AC is on now. Again, you assume AC has turned on. Enjoy the cool breeze from AC or imagine so. Car has access to its parents attributes and method. Along with that, it has its own attributes and methods too. It is privileged class. I will define an instance my car, which is a car with attributes, fuel petrol. Transmission automatic and with sunroof, yes. Fuel is inherited property from class vehicle. Let me print mycar dot fuel and let me try both methods, car dot SAT. This is an inherited method from its parent class vehicle. Along with that, I will use cars own method, car dot switch on AC. Now both engine and AC turned on or assumes. This is how attributes and methods are inherited from parent to child class. If you want to know how to inherit the properties from your parent class, you need to consult your nearest lawyer. Python cannot help in this regard. We have converted one horror movie into romantic jolly ride in car. I hope you felt inheritance super easy. Same goes with the next concept that we are discussing in next lesson. 41. Encapsulation: Second concept we are exploring in this lesson is encapsulation. The fancy word sound like encapsulating you inside confusion. No, it's not that complex as you think. It's easy concept that you know very well. Assume you have some confidential document or note with passwords, how will you handle it? If that was me, I would keep in such a safe place that even I search for it later when I need we don't keep them open in public place. When you have some private document or information, first thing we do is wrap it inside cover or back so that the information is not easily visible outside and then lock them inside the safety drawer. That means you keep it covered or encapsulated to hide from public. Only you or your authorized trustworthy person, maybe your parent or business partner would know how to access such data. This is something we are doing since childhood. We used to hide things from siblings or elders. What you used to hide differ from person to person, but the thing is we have done it. This simple concept that we are doing since childhood has the fancy term called encapsulation. Simple term, encapsulation is hiding from the public and giving access only to authorized person. In VOP terms, encapsulation is controlling the access of the object class. No matter how much we say about it, you will understand when we use it in example. Let us see how we do that in Python. For this concept, let me define class bank account. Bank account details is something you do not scream. This is my account number. This is balance, and this is my password. There is no need to keep balance private, but no one like to insert themselves showing balance. All this information need to be private and accessed only by you and other authorized person. Let us define two attributes, account number and balance, and both these details must be hidden from public and access it privately by you or authorized person. So both these attributes need to be encapsulated. There is a way to secretly tell Python that the attribute is confidential and need encapsulation. Provide double underscore before attribute. Self dot underscore underscore ac number is equal to ac number. Now OOP no account number is confidential, and it cannot disclose your balance too, self taught balance also need encapsulation, so provide double underscore. We have defined the instance and encapsulated it. Now encapsulation does its job too well that it don't even disclose the details to you. You cannot access or modify the values at any cost or influence. If you don't trust me, check it by yourself. I define an instance, my account, which is class bank account. I need to enter account number and balance. This is top secret. No one could say it, but I'm sharing it in public. My account number and balance is defined. I assume you have not watched it. You can assume yourself, which currency it is. Now access my account dot Balan. Python say there is no such attribute. Check underscore underscore balance if you think that may work. No, just by giving double underscore, Python understood very well that data is confidential and Python is good at keeping secrets. It says there is no such attributes. Good job, Python. Today, I have understood even Python lie, but for good cause. Python don't allow anybody to see the details and no one is allowed to modify the details, even you. What we must do is allow the VOP to access the details in controlled way. I define a method, credit. I want to credit some amount to the account. Self amount and add the amount to the balance, you need to strictly use double underscore. Self taught underscore underscore balance is equal to self taught underscore underscore balance plus amount. When you add the amount, there must be a way to even withdraw it. Similarly, another method debit to withdraw some amount. But what if guy tried to be over smart and try to withdraw more than the balance? For that, put if condition, if amount is greater than self dot under scronoscoe balance, you need to tell insufficient balance, else, otherwise, deduct the amount from the balance. That's all okay. But Python, don't allow me to even check the balance. How can I check it? You need to create a private method to check that. Define check balance with no argument, only self, and return the balance in the style of encapsulation. Self dot underscore underscore balance. This is called accessing and operating in controlled way if you have feared hearing these terms. Now I define my account with 2000 units balance, and then I will credit 1,000 units more. I can add any amount just by typing values here even in millions, but I don't want to make joke of myself. Now, what should be the balance? Is it worked well? I will try to withdraw 4,000 units and want to check balance. Python says insufficient balance in front of me. Don't know how it reacted inside. No change is done for the debit, hence balance should remain 3,000. Now tell me, guys, is there anything called difficulty in these concepts? They are just creating the panic using the high standard words, inheritance, encapsulation, but they are very easy concept. Shall we move to the next concept? It is encapsulated inside the next video. 42. Polymorphism: The last concept we are learning in OOP, which is also very simple but horrible to hear is polymorphism. Doesn't it sound like something used by doctors or biologist? If you felt so, you have got pretty good intuition. Yes, this is a biology term. Chance is there anyone from biology background among the audience, then they know the meaning of this term very well if they attend their class and I assume they did. If there is no one here, then I can speak with more confidence. In biology, polymorphism is state in which an organism that can exist in different form, that doesn't sound cool for non biologist. Don't make it unnecessarily complex. It is the simple task that we do almost every day except Sunday. Have you ever been multitasker? Sometimes we need to be multitasker when we are balancing the home and office. You may be cooking or doing other work at home while attending the office call. Yeah, I know, and I don't tell these secrets to your boss or professor. Moreover, even they do such multitasking. Don't you think they are human beings? You perform multiple roles in your life every day? You are a programmer when you sit in front of a computer, Chef when you are in kitchen, strict s to reportees obedient husband in front of wife, sleeping monster on Sunday. We play all these characters being just one person. This simple concept is called as polymorphism. In Python, polymorphism is using the same function or method inside different class to return different outputs. We shall see how we do that now. As the term polymorphism is derived from biology, we consider example from biology, precisely from Pharma. I know you hate medicines, but in modern days, people started to consume more medicines than foods. These medicines have different class. We use different class of medicines for different problems, like in technology, even they use fancy difficult to digest terms for even simple concepts. I will define few of the class of medicines. Start with defining the class analgesics. I don't define any attribute here. We already learned how to define attributes. I don't want to repeat it again and again. Scope of this session is to learn polymorphism. I directly define a method, what it does, to define what it does as its name says. What analgesics do is relieve pain. I print that. If you feel headache after learning any concept, you can go for analgesics, but only after consulting your physician. We have defined one medicine, define another class of medicine, antibiotics. Even it has say method, what it does that print treat bacterial infection. The method, what it does is not the private property of analgesics, even antibiotics take it. That doesn't end here. The next class antipyretics, also use what it does. What it does is reduce fever. Finally, antihistamines that treat allergic reactions also has method, what it does. Now we have four class. Now I will provide one instance each to these classes that are commonly used. You can define more if you are pharmacologist. For analgesics, I assign ibuprofen. Azithromycin for antibiotic. For antibiotics, let's take paracitomol and finally, tysin for antihistamines. These are not my prescription for any health issues, by the way. In polymorphism, the method is same. That is in this example, what it does. The same method is used by multiple classes. The method, what it does is a multitasker like. If you ask parasitamol dot, what it does, Python first check which class parasitamol belongs to. Acetamol is antibiotics, so it return the method of antibiotics, that is reduced favor. If I ask what do azytomycin do, it reply treat bacterial infection because it is an antibiotic. The method is same, but applicable for different class. Such state of method to exist for different class is called polymorphism. Again, I asked the same question, is there anything difficulty here? No concept in this world is difficult. We make it unnecessarily complex. I want to conclude one thing for you. Complicated looking term might have very simple meaning. How is your learning journey? We have come to the end of the course, but the new beginning of your Python journey, see you all in farewell party. 43. Last Note: Welcome back. And this isn't just any regular session. This is not the technical session like previous ones. But the one where we are going to celebrate your commitment to learn, you made it to the end. This is the time to put on the party hat. But seriously, feel free to treat yourself later because you have earned it. First thing first, give yourself a big pat on your back. You seriously deserve it. You have traveled all this way through data types, conquered loops, tamed functions, and batted bugs. How was the journey if you look back? I hope you have enjoyed learning new things. Now that you have reached here the end of the course, you might be wondering, what's next? You have finished the course. Does that mean you are done with it? This is actually just the beginning. Think of it like this. You have finished first level of the video game, and as the reward for unlocking the new level, you have got a sword. That is your Python skill. Have got a new weapon. Before you build the next Instagram or Netflix, you got to sharpen your new skill. But how can you do that? There is a secret to sharpen your programming skill that is not a secret anymore. Here is the key to take your coding skill to next level. Practice in the online platforms, I suggest you to practice problem solving in competitive coding platforms like HackerRank, code chef, Hacker Earth or any other popular coding platforms. If you're particularly interested in data science challenges, practice in Cagle. This step is very important. These online coding platforms are like the gyms for the programmers. It is where you get to flex your coding muscles and learn to solve real world problems. While also competing with others. You are not expected to maintain the great rank from day one. It is not just about winning, it's about learning, growing, and leveling up. Every problem you solve, every error you fix is like leveling up in the game. You get stronger, you get faster, and you get better. It will improve your problem solving skill, increase speed and efficiency of your coding, increase confidence, and last but not the least, it will help you to crack the programming challenges of recruitment process. But I want you to remember something that is really important for a programmer. Don't rush. Coding is a marathon, not a sprint. It's okay if you make mistakes. It's okay if you get stuck with the problems. The key is to keep going. Take your own time, learn at your own pace, and most of all, don't forget to have fun. Whatever you do, enjoy it. And when it comes to Python, it is not just a tool, it's also your playground. You can play around, experiment the odd idea you have, and enjoy it to the fullest. Let's talk about community. Even this is important because let's be honest, sometimes coding can feel a bit lonely. You will feel like it's just you, your computer, and that annoying bug that just won't go away. It can be frustrating sometimes. I will suggest you to find a body or group of people. You're not at all alone in this technology driven world. There are millions of coders out there, maybe just around you. They are just like you, learning, struggling, and celebrating their wins. Find them, join forums, find groups. Once you get them, ask questions and share what you know. You will elevate your skill level while helping others to solve their problems. Whatever comes next on your way, whether you're starting your own project, doing coding challenges or maybe even getting into data science, I want you to remember, coding isn't just about writing lines of code. It is about solving problems, being creative, and having the courage to keep trying even when it gets tough. I strongly hope you will shine like a charm in programming world. Always excited to see your success. If this course has laid at least 1 stone to the foundation of your success, that fulfills the purpose of this course. The digital world is small and our paths may cross again. Maybe in next course, or maybe I will hear about something amazing you have built. Until then, keep creating and most of all, keep having fun. At the end of the day, you must enjoy whatever you are doing. Thank you so much for being with me on this journey. Now go out there, make some magic and remember quote like nobody is watching. Love you all and Bye bye for now.