Learn Python FAST! Full Fast Track Python Programming course - Zero to Hero Python training

1. Intro: Welcome to the Python programming course. My name is Mark Bukowski and I thank you for choosing this training. I've been working for many years as a DevOps and Cloud administrator using Python as a tool to automate many mundane tasks. Python is very useful and extremely popular programming language, and it's used in AI, in automation, networking, and many other fields. This training is designed to take you from having zero or very little Python knowledge to complete understanding as quickly as possible and we will learn Python by writing code and building stuff rather than just talking about it. In the second lesson, you will not only have already Python installed, but you will also have your first program written. If you are starting your Python journey from scratch, I suggest watching these videos in order as they appear on the platform, I mean, because jumping straight to a random video might be a little bit difficult because some of them may rely on the concepts discussed in previous materials. I hope you find this training informative and I thank you for choosing this training. 2. Python installation / first program: In this video, we will install Python. We will see what Interactive Shell is, and we will also write our first program in Python. Let's start from the installation process then. We'll see how to install Python on Windows, Linux and Mac, and I will start from MAC because that's the easiest part, and it's the easiest because the Python is already installed on your Mac. This is my Max terminal, and you can check what version of Python you have installed by typing either Python. Version, it's dash dash version or Python three dash dash version. You can see I have Version 3114 of Python installed here. I didn't do that. It simply came with that Python installed. There's also shorter version of that command. You can run just Python one dash and V, and then Python three. Regardless of operating system, you should always check both those commands. The reason that one might work and the other will not is because Python has two major versions. It's Python version two and Python version three. That first letter is so called major release, as you can see, it's Python version three, and that's the Python we're interested in. Now, if you have older Mac I mean very old MAC, you might have only Version two of Python installed. Which most probably will be shown when you run this command, Python V. If that's actually the case for you, then you need to install Python in version three because that is the version we are going to work with here. It's very easy. You can simply go to Google and just type Python Mac Install or something similar. And if you go there to downloads, you can see download the latest version for Macs. So you just click this button and follow the instructions. But being on the Mc, it's probable that you're using the Home Brew package installer. Then you can run just Brew update and Brew upgrade. And once that is done, you can follow it with Brew Install Python three. And this command will install Python inversion three on your Macs. I have it already installed, so I will not run it, but this is the command you are interested in. That's Macs D. I will show you now how to install it on Centos seven and they specifically chose that old operating system so you can see exactly what I'm talking about that Python two, Python three. If I go to that Centos, let's go to Santos. This is the Sent server. If I run Python version, I've got Python in version two installed here. It was pre installed as well. I didn't have to install it, but it's version two. If I run Python three version, it says command not found, but I need Python three, so I have to install it. It's super easy though. It's just pudo hum update first, just to make sure that our packages are up to date. The information about packages is up to date. And once that's completed, as you can see, it's complete, you can just run sudo, you install IP three. Yes, firm. That was quick. Now let me clear that again. If I run Python version, I've got Version two. It's still there. But if I run Python three version, I have also Python in Version three. That is very important to understand because we want to run the command that refers to Python version three. I hope that makes sense now. On this particular sentence, I would have to run always Python three. But it's not always the case. If we jump to Ubuntu now, that's the other server, that's the Ubunto. So this one, the first one. If I run Python version, doesn't show anything because it doesn't come with Python version two installed. But if I run Python three version, it has Python three already installed. I didn't install it. It just came with this Python. But you might be on Santos or boom to server, and you run Python, this first command, and it will come back with Python in version three, because it's very easy to create a so called sim link for this command to refer to that command. I know it's a bit confusing, but both those commands would give you the same output. People usually don't install Python in version two anymore. People usually need only Python version three. What is important for us, we have to know which command we can run, so we work with Python in version three. As I said, this Ubuntu came with Python three pre installed. But if I didn't have it installed, the process would be very easy. The installation process would be very easy anyways, and it's basically the same as I sent seven, only Ubuntu uses at packet manager, which means we have to run sudo UT update first. We used to run sudo Hum update, if you remember, on Santos and Sudo UT update here. Okay, that's completed. Once that's done, we run sudo upped install Python three. Instead of Hum, we just use UT. That's the only difference. Enter, you can see it says Python three is already the newest version, at least from the official installer package installer, so it didn't do anything really. But that's basically it. So we've got MacOS and Linux. Let's check the Windows now. On Windows, I can open terminal by typing CMD. This will open my terminal, and they run the same command. Python version, says Python not found. Always remember to run the other command Python three version. But it also says Python not found because Windows doesn't come with Python pre installed. So we'll just find one. We'll go to Google, Python install Windows, something like that. We just go to first Link. Downloads. And it says, download the latest version for Windows. That's what we want to do. Click download. Once it's downloaded, I just click the Ex file. Normal installation with just one little difference right now. It says, add Python ex to Path, and that's what we really want to do. Because if we don't do that, it's possible to do it later on, but it requires some knowledge that we can just click the bottom and that's it. We don't have to worry about anything later on. So once you have that ticked at Python exit to Path, we can just follow standard installation process for Windows. I click Install Now, then just close. The other little thing, if you go back now to your terminal, and if you repeat those commands like Python version and Python three version, you can see it still says Python not found. You simply have to close it and just reopen it, C and D. And now if you run it again, Python version, you've got Python three installed. And if you run Python three version, you can see Python not found. And now you see my point. You always have to run both commands because Windows behaves completely different way, even though it's Python in version three. You have to run standard Python command rather than Python three. But as long as you know which command to run on your operating system, that's fine. Doesn't really matter. All right. So that's Python installed on all operating systems. And now we have Python installed, but so what? How do we work with it? So the first option is that interactive shell I was talking about. And maybe let me close that. I will terminate those servers as well. We don't need them anymore. I can just use standard Ubuntu that I have locally here. Here I have to run what Python three. Version. It's the same version that I had in AWS on the other server. It's different ubuntu but the same version. So if I now just run Python three without that version, just Python three, this will take us to what's called interactive shell. And the interactive shell is a place where you can write instructions for Python to process. And the most popular task that you usually do when learning any programming language, not only Python, but any, is to display words hello world. And in Python, we can do it by using print function. So it's print, and then function has to have those brackets. So what we can do inside those brackets, inside quotation marks, we can write Hello world. And if I click Enter, Python, displays back the words that I put in those brackets. The print function is simply instruction for Python to process anything that we include inside those brackets and display the result back on our screen as it did here. And in this example, Python didn't have much to do really, but that print function can be used for many other things, like we can use it as a calculator, for example. If I type print, and now let's say three multiplied by four, don't know, we use the asterisk to multiply numbers. So if I clcanter now I get back 12. Python first processed whatever was in those brackets and only then displayed the result back on the screen. The same if I want to divide something, let me just use up arrow, I can do 2/7. So this forward slash is used for division in Python. If I clcanter, I have the result back. You might have noticed that I wrote those numbers without quotation marks, though. While previously that hello world, I had to include that inside quotation marks at the beginning and at the end. This is how Python processes different data types, and we will learn about those data types more in dedicated video. But for now, I wanted to show you that you can do stuff that at first sight might not make much sense because if I run, for example, something like I don't know, print, and then I don't know, ten times hello world. Might think, that's silly. But if I click Enter, Python simply displayed ten times string hello world. Yeah, because those words here inside quotation marks, they're called strings in Python. Somebody might say, that's cool, but we were supposed to write a program here, if I remember correctly. Yes, that's correct. And that's what we are going to do now. But that interactive shell, it's very useful if you want to, for example, test quickly some stuff, if you want to check some commands, but it allows you also to run multiple lines. It doesn't have to be one line, but it's simply a tool available within Python. You will find very, very useful later on. But for the time being, let's get out of this interactive shell to get out, we can actually use another function and its function called exit. Because it's a function, we always have to follow it with brackets, we don't have to put anything in those brackets. We can just click Enter. The other way to exit the interactive shell is Control D on Mac or Linux or on Windows, you can type Control Z and then click Enter. So how do I write a program in Python? To write a program in Python, I just need to create a file with dot PY extension. That's it. Let me clear that. And I can use any text editor that I want. It doesn't matter which one I use. In Windows, you can even use note but on my Ubuntu, I can use VM, for example, or, you know what? Let's just go first. What is text editor? Okay. Let's just use this text editor, and I will write what? Print. We had Hello world. But I can then write like what? Print to divide it by seven. I can also print maybe 20 times my first program. My spaces. And now I can save it. Mark. Save. I showed up here, so I can close it, but how do I run it? I run it using Command Python three and then path to this file. 1 second, let me just control see where home. I will go to desktop. And this is my file. This is this file, Marc dot py. Now I'm in the same folder, I'm on the desktop, so I can just run Python three, Marc dot py. If I click enter, I can actually 1 second. If I run cut, Mark Pi, it will show me the commands. I will show me my program basically, so we can see it followed those instructions. It first printed hello world, then it divided two by seven, which is this, and then it printed 20 times my first program. Without spaces, we could add space here at the end. You know, the formatting isn't perfect, but never mind. And I know it might be very simple, but that's basically it. That's your first Python program. 3. Data types: In this material, we will talk about data types used in Python. The most popular data types are string, integer and floating point number. So let's start with the string, maybe. Python string is a collection of various characters that you can find on your keyboard that we then enclose in either single or double quodes. And those characters can include letters, numbers, and special characters like question mark. Spacebar is also considered a character and can be used as a part of Python string. As long as they are all inside single or double quodes, Python will consider that as a data type string. And now you can see this plate some examples of string data type and note that they are all in either single or double quotes. Let's talk about the integer now. Integer is simply a whole number. It can be a positive number like ten. It can be a negative number like -200 and zero is also considered an integer. As long as it's whole number and it's not in a single or double quote, it will be considered by Python as integer data type. Then we have floating point number, and floating point numbers are simply fractional numbers like 2.5 or I don't know, 8.44, something like that. And they are also not inside any quotes. We just write them as they are. Okay, but let's play with those data types directly in Python because, you know, seeing just the theory does not explain it well enough. We have to see it in action. So this is my UBT server, let me open the terminal. And let me type Python three. This opens our interactive shell, and if you don't have Python installed on your machine, please see the previous video where we were installing Python. I've got my interactive shell and I can print. This is the function that we can use in Python to process the data within those brackets. So if I just type hello world, there's not much to process. It simply displays back hello world. However, there is another function I wanted to show you and it's called type. At type, we just replace print with type. This is a function in Python that shows us what data type it is for Python. So if I click Enter, you can see STR, which really means string simply. So string are all those characters here inside the quotes and note we included the space as well. When I click Spacebar, it's still considered a special character. It can be part of the string. If I try to check how Python sees, for example, I don't know, whatever. These some numbers and then some special characters as well. If I click Enter, it's still a string. So even if I put the numbers or special characters, as long as they are within either single or double quotes, it will be still a string. Let's try now some numbers. Type maybe ten. Now, Python considers that as an integer. We have only INT, but that means really an integer. Now if I try the same with let's say -200, that's still an integer. And if I try zero, Python still considers that this data type inside, it still considers it an integer. Let's jump to floating point number. If I type 2.5, now we have float. The full name for that data type in Python is floating point number. Anything that has that dot notation is really a floating point number. Because if I type 2.0, note that it's still a floating point number. But if I type just two, now we've got the integer. So it's not really about the value that is stored there, it's about the notation. If we've got that dot notation, it will become a float. If there is no dot, it's considered an integer data type. But now let's go a little bit further. What if I type, maybe print first to see the output five times hello world. What will happen? What do you think? Let's click Enter. Python simply displayed string that string because we've got those quotation marks. I displayed that string five times. But what if we now check what data type it is? If we use type function, what do you think we will get? Let's click Enter, and it shows us it considers it a string, which makes sense because it's very long output, including some spaces, but it makes sense, doesn't it? It looks like a string. It's simply now much longer string. It multiplied string five times, so the output is still considered a string. What if I do now type 5.0? I'm trying to multiply five times hello world, but now I will use floating point number rather than integer. Let's click Enter. We've got type error. Python tells us, I can't multiply sequence. Sequence, it means really that string. I can't multiply it by something that is not integer. You can't multiply it using that dot notation. And that's really important to understand because there are some operations that are allowed in Python, and there are some operations that are not allowed. Because consider a situation where I'm trying to do, let's say, I don't know, 5.77 multiplied by hello. That would also make no sense. I mean, this notation actually makes sense, but Python simply refuses that operation because it can see the floating point number, and it only allows for that whole operation as long as this part is integer and not floating point number. So there are some limitations that we have to understand within Python. Somebody might think, Okay, but for example, this is allowed. Print -200 is integer, isn't it? So I should be able to multiply using this operation. If I click Enter, well, there is nothing displayed because it's negative number. But if I check type of that output, Python doesn't mount. It says, it's string, even though, you know, it's nothing there, but this will be allowed. Same with zero. Still fine. Let's check a few more examples. Let's do print two by two, maybe spices here, easier to read. We've got four. Let's print two, multiply by 2.0. So we've got integer. And we've got floating point number. If I click Enter, now we've got 4.0. Why is that? Because result of this, if we multiply one integer by another integer, the result is still an integer. If we multiply integer by floating point number, the result will be floating point number, and we know how to check that. We can just use that type function. So if we do type two by two, we can see it's integer. If we do type two by 2.0, we can see the result of that operation is considered by Python as a floating point number. What if I do print two by this? What do you think? Now, this became a string because dot is also a special character that can be a part of the string. What Python will do now? Click Enter. You can see it's called string concatenation. It simply displayed this string twice, 2.02 0.0. It didn't do mathematical operation. It simply displayed this string twice. What will be the data type as a result of this operation? As you might have guessed, in this example, it is actually a string because this is I mean, this string is similar to this one we had with Halo world. We did exactly the same operation here. Only this one made a little bit more sense. But once we start doing this, it might be not clear at the first side, but that is not a number anymore. This now is just a string. So a sequence of characters. So yes, that's really all I wanted to say today. I just would suggest to play with those data types for a while, because the better we understand what is allowed and what is not allowed in Python, then the more efficient we will become in the future when dealing with errors in our programs. 4. Variables: Now I want to talk about variables. What are those variables? They are not specific to Python. They are in most programming languages. You can think of variable as a box or bucket, let's say, where you can store some stuff, and what is that stuff that you can keep there? It can be loads of things actually. It can be a basic data like a single string, integer, or floating point number. But it can also be some more complex data like lists or dictionaries or even entire functions. All that stuff can be stored in that variable or in that box or bucket as we call it. And as if we do with the bucket or a box, we can store some stuff, but later on, we can take this stuff out and put some other items in. Let's see exactly how it works. This is my Ubuntu, and I will just open terminal, and we open interactive shell with Python three command. I will write something like X, equals, string, Mek. So I've got double quotes, so it's a string. And what I did here, well, I have to click Enter. Now, what I did, I assigned that value, that string, Mk to variable that I called X. That's all we have to do. We have to type the name of the variable and then what we want to put there. So I can make another variable, maybe Y, and it will be equal to one, two, three. Let's make yet another one that equals, let's say, 500 or 500.5. Now when I print value for X, it will show me that this variable X stores string of characters RK, and we know it's string because we remember the function type. If we do type X, Python remembers that this is string. The same if I do print, Y, we've got the other value. And then we can also do mathematical operations. If we store, for example, integer and floating point number, I can do things like print Y plus Z. That gives me six to 3.5 because it added what's inside Y and what's inside Z variable. We can also multiply integers by strings. So if I do print, Y multiplied by X, I will have string Mek displayed 123 times. But what if I now change those values? These are called variables for a reason. I can simply put there whatever I want. So maybe let me clear that and I will now say X equals one, two, three, but it's in quotes. So this will be a string, and Y will be, again, maybe 500.5, but it will also be a string. If I print it now, X plus Y, Python will do string concatenation. It will take those characters, one, two, three, we'll display them here, and then we'll add those characters, string of characters, which we can see here. And if we do type X plus Y, we now can see this is no longer integer or floating point number. This is treated as a string. The other thing I wanted to say about variables is that they are case sensitive. If I put ABC equals Marek. And ABC lowercase equals one, two, three. Then if I print ABC, it will give me something different than if I type ABC lowercase. Okay, let's press Control L again. We will clear that out, and I will tell you a secret which helped me a lot with variables. Let's say we have something like that. X equals 100. Then we write X equals X plus one, and maybe some of you will say, Mark, that doesn't make any sense, but in fact, it does. If we print X now, we have 101 because we can't really treat this as mathematical operation. What we do here and what made me understand what's going on here is to read those instructions from right to left rather than from left to right, as we normally do. So we take 100 and then we assign that 100 to variable X. So we read first what's on the right. It's 100, and then we put it in our box in our bucket, and our bucket is called X. And then what I do in the next line is completely separate operation, but I will read it again from the right. I take the current value of X, I add one to that value. So I've got 101, and then I repeat the operation. I take that 101 and assign it as new value to my bucket. This is my new item in my bucket, and the third line is again, completely separate operation. I print the most current value that I store in my bucket called X, and it's one oh one there right now. So if I repeat it again, now, you might have guessed, I will have 100 too. So once you start reading them from right to left, then, well, at least for me, it made it much easier to understand what's going on, the entire process. And I think that's all for now, make sure you understand it very well before we progress even further. Thank you. 5. List and Index Position: In this material, I want to discuss yet another data type in Python, and it's called a list, we've already learned about variables and how they can hold information like integers or strings. Let me open the terminal. Let's open interactive shell. For instance, if I declare X equals Marek, and Y equals one, two, three as an integer, then I can retrieve that data by using print X or print Y. However, storing just one value per variable can be very inefficient and challenging in certain scenarios. Thankfully, with lists, we can store multiple values in a single variable. I can write something like this. First, maybe Marek. Then we could add that 123, maybe I don't know, 500.5 we had previously. Now again, one, two, three, but as a string this time because it's within the quotes and maybe also 500.5, but also as a string. We will enclose it in brackets in quotes or again. Here I have five different pieces of information. Ideally, I'd like to keep them all in one variable rather than creating five separate ones. Sure, with just five values, it's not that challenging. But imagine if I wanted to store 100 or even 1,000 different values, creating separate variable for every single item isn't very efficient or very clean. This is where the last data type comes in handy. What I can do now, I can enclose all those values that I need inside the square brackets. And then use commas to separate them. I can include or mix and match all data types, as you can see, because I've got here a string, here is the integer. Here we've got floating point number, et cetera. They can all be in the same list, and now we can assign all those values to one variable called X. I mean, I will just call it X. And once I hit Enter, all that information is saved in my variable. So if I print X now, I can see my entire list. However, displaying all that information at once isn't usually necessary or isn't what we really want when writing a program. Typically, we only need a specific data from that list, maybe one item or maybe a few items, but not the entire list. This is where index position comes into play. An index position is simply the current position of each item within our list. It's important to note that index positions start from zero, not one. The first item in our list, string MA we'll have an index position of zero. Then the second item will have an index position of one and so on, which means our list has what? One, two, three, four, five items. But the index positions will start from zero and end at four. This will be index position number four. The question is, how can I retrieve a single item from that list? That's exactly what an index position is for. So I can do something like print X, and then I just use its index position. Let's say I want to retrieve the first item, Mek, string Mrek. It has index position of zero, so I add exactly that. It's index position in square brackets. If I presenter, I've got only first item from my list. As you can guess, if I use index position number one, I will actually get second item from the list. It is a bit confusing, but you can get used to it, and my last item in my list will have index position number four. So I have to use four. I can also perform some, let's say, mathematical operations as we did with single items. I can do something like that. This is the item with index position number one, which is 123 integer, and I will add again the same item. We should have 246, 246. If I add, maybe here we change to last item, and this one will change to first item, I will have Mark 500.5. Why is that? Because they are both strings, Mark and this 500.5. This is enclosed within quotes, so this is read by Python as a string. Python performed string concatenation, it displayed Marek and then added those characters. It simply created longer string of characters. But now interesting thing is I can also count from end of my list towards the beginning. I just use negative numbers. Minus one, index position minus one is the very last item in my list, it should be 500.5. Second item from the end of my list will be this one, one, two, three, but this is string. It's not integer like here, so we can check that. We can also double check the type, which indeed is string. More thing I wanted to mention, we can also pick multiple items. For example, we can do something like that, colon and two. What I do now, I want to retrieve all values from my list that go from zero up to index position two, but it will not include that index position two. To make sense of that, let me click Center. This entry means go up to index position two, but not include it. It will take index position zero, we display it. It will take index position one, will display it, we'll go to index position two. But this notation says do not display index position two. But if I do something like that, I will remove column here and we'll add it after the two. This means go from index position number two to the very end of the list. If I click Enter now, this time, index position number two will be included in my output. So it's zero, one, two, and we can see this item is included in my output. Then we have one, two, three, and simply it goes up to the end of the list. These are the very basics of how we can work with lists in Python. And I would suggest you play with it as well, especially with this item because it's a bit confusing, at least for me. And just to double check, we can also do type for that X now, which shows us that new data type or data structure, sometimes it's called that it's called list. That's it. Thank you. 6. Dictionary method: In this material, we will learn how to use something called a dictionary in Python. This dictionary in Python allows us to work with something called key value per. I know that doesn't explain much so far, but don't worry. I will show you what it is all about with examples because that's probably the easiest way. To explain this, let's think about what dictionary actually is and how we can use such a dictionary in our daily lives. Take, for example, an English to Spanish dictionary. Let's say we want to find out what is the equivalent of English word hello in Spanish. So we open our dictionary to the page where the English word hello is located, and we can see that in Spanish, it's a word O. And this is exactly how a dictionary works in Python as well. So that word hello that we're looking for is our key. We want to translate that word into Spanish. But at this stage, we don't know yet what is its Spanish equivalent. So we search for the word hello in that dictionary, and once we find it, we will discover that in Spanish, it is Ola, and that word Ola is the second part of our key value pair. Hello is the key, and the Ola will be our value that we are looking for. This value represents the meaning, and it is simply something we are interested in. This is the value we were looking for in our dictionary. Means we need to know that first part, we need to know the key, and we know the word hello already. We just don't know what is the Spanish equivalent of that. But since we know what it is in English, by searching through a dictionary, we find its Spanish equivalent. So let's create such dictionary in Python. And since we enter words in Python in quotes because word like hello or Ola will be a data type string means sequence of characters. So we write something like Hello in quotation marks as a string, then column and then quotation marks again for another string, and that other string is Ola. So we write the key, the column, and the value, and maybe we want to add more key value pairs. What else should we add? Maybe we will add the word goodbye. What we have to do, we will separate that with the comma, and now another per. Goodbye, and we will type it Spanish equivalent, which is Adios. Maybe another one, let's say apple, but we will separate again with the comma. Comma will separate each key value per, and now another entry will be Apple then colon and what its value. And in Spanish, it's manzana. And maybe one more, I don't know, bike and in Spanish, it will be Basileta we could carry on. We could enter as many keys like these hello and O key pair values. We could enter as many of them as we want. We can even input all possible words in both languages, creating our own full English Spanish dictionary. All right, but how do we access a value for a given key now in this dictionary in Python? In the book, we open to the page where the word hello is and that's it. So how do we search for that word in Python? There are many possibilities here. Let's look at a few of them. First, it would be nice to save it as just one variable. Our entire dictionary will be saved as just one variable. Remember how in the previous episode, we saved the entire long list as variable X. Here we can do the same. But to save our dictionary, we need what's called curly brackets. So we saved our list using square brackets, and here we need to save the dictionary using that curly brackets. It's curly bracket at the end, curly bracket at the beginning. Then we can just save it as X equal and all those entries that we want to keep in our dictionary. Let's just click Enter and the question, how do we search that dictionary? First, let's try to let's see what happens when we just print the X. As we can see, Python will display the entire content of the dictionary. That is all the key value pas that we have saved in it. Well, that's nice. But if we save 20,000 words in it, let's say, that won't be very helpful, will it? So let's search for only the word that we are interested in. Let's type again, print X. And now, just like in the previous material on the list, where we enter the index number, for example, print X and index position one, here, instead of that index number, we will enter our key. Let's say we search for Hello. What will be the Spanish equivalent of hello? So we will paste here in quotation marks still Hello. And now when I press Enter, we see that it shows us the value for key hello. This is the information we are interested in from that key value per. The key is our English word hello and the value is its Spanish equivalent. O. Now, let's say we want to find out what the English word apple is in Spanish. We do exactly the same. We can do the arrow apple and we know it's manzana. But I mentioned other ways to work with dictionaries. The alternative way would be to use something called a method and what that method is anyway. In short, I can say that both lists and dictionaries, they will both have something called methods that might help us to perform certain operations on these lists or dictionaries. To check which methods are available for us, we can enter something like print. Then help and then the data type, which is dictionary, the ICT. It will display us help regarding dictionaries. So if I press Enter, you can scroll down. You can see get method. For example, there is another one called items, keys. We also have values, but let's maybe return to our task. So I can use a method by writing print again. A X, then dot G. That's our method we want to use, and then in the brackets word hello. That will display us also the Spanish equivalent. But how did I know to put it in the brackets? Maybe, let's go back, sorry. If we go to that help to get method, and these are the possible values we can use in that bracket. You can see the key. And if we use the key inside the bracket, it says, return the value for the key if key is in dictionary, else, default. Basically, I need to put my key. What is my current key? I'm looking for. But someone might look and say, Mark, this is exactly the same what we wrote without this method. We got exactly the same thing when we printed this above in square brackets. It's exactly the same output. And at the first glance, it might indeed seem so, but using methods has a significant advantage in programming, especially regarding how it handles errors. Let's say I type something like print X, but hello, maybe I mistyped it. I missed one L in our key. Now in a presenter, we can see that Python throws out something like trace back, mouse, blah, blah, key or hello, it looks messy, doesn't it? But now let's do the same but using method. This is our method. And again, let's say I have missing L and press Enter. Now we simply get none, which is the notification that such key does not exist, and that's it. And if it's part of a longer program, this kind of output is much cleaner and much more predictable than the previous messy one. If we look back at the Python help regarding this method, we search for if we use the help function again, if we scroll down, you can see where this non is coming from. If we type the key and the key is in the dictionary, we will get the value of that key. But if the key is not in the dictionary, it will return that default option and default equals none. That's why we get the non response from Python. But I started from the pretty difficult one, to be honest. We also have those keys, those items. We've got values and look at that nothing is actually needed in the brackets. Same here, keys or items. Don't have to put anything inside those brackets. So maybe I should have started with those ones. Here. Let's go back, pressing Q. And now let's do print. Again, X dot, maybe keys first, Keys and then brackets, but nothing is needed in those brackets. IpressEnter and Python returns all the keys that we have saved in the dictionary. So you can guess if we change it to values, we will only get the values, which is the second part, yes. These are basically all the English words we have in our dictionary, and these are all the Spanish words we have in dictionary. Let me clear that Control L. Let's get my C. Now let's trade that other function called items. We change again that method to items, plus Enter and Python displays pairs of key values, but each of these pairs is in separate parentheses. This can be very useful if it's part of the longer program. As an exercise, let's maybe create a different dictionary at all. Maybe this is the information about the car that I used to have years ago. I want to keep information about it as a dictionary. So I can do something like car equals curly brackets and then all the information about that car. Let's say brand was Volkswagen. No, comma, that's the first key value per brand is the key. Volkswagen is the value. Now the second information, second key value. Let's say model and the model, it was Passat Volkswagen Passat. Now, another one, maybe, it was manufactured and it was 2002, and maybe how many miles it had. It had 120,000, if I remember right. As you can see, in the dictionary, you can store not only strings, but we can also store other data types like integers. We have here two integers. The year is 2002, and the miles, the value is 120,000. But as you can remember, integers, we don't use quotation marks for them, neither here nor there. So now I save it, pressing Enter, and then I ask you to practice with this new dictionary. If we print car, that will give us all information about the But now try and use that other ways to access the key value pairs or individual key or value. So maybe car get model, and I will let you do the rest just the way we did it in previous example with the English Spanish dictionary. I hope everything will become clearer when you complete this task and when you approach it yourself. So thank you for watching. 7. 'for' loop: This video, I wanted to talk about something called four loop in Python. Maybe instead of trying to explain what it is with words, it would be better to simply look at some examples. Let's open our Python again, the interactive shell, and let's create a list with six elements. And it can be one, two, three, four, five, six. Now let me create a four loop for those items. So I will add four I in and now our list, what it does, you will see shortly and we will discuss it. But for now, let's just write it four I in that list. At the end, we will add colon and we press Enter. Now we need something called indentation. So you have to press either tab or you have to press space multiple times. I will press Tab, maybe. Tab will create like four spaces for me. This is called indentation. You have to start further. Not this free space here is the indentation. All right. We write print I. Now press Enter and you will have to press Enter one more time. You have to press Enter twice because if you press just once, Python will think that you want to write yet another line rather than execute the program. We press Enter twice, but what we have as a result, as we can see, each of the elements we had in that list is displayed now as a separate item, and each of those items appear on a new line below. Let's think about what exactly happened here, what this four loop did exactly. I think it's easiest to understand if we read this instruction backwards. I mean, this is the instruction, first instruction for I in one, two, three, four, five, six, what this four loop first checks, if this object, it will check if this object is iterable. Iterable means it's anything that it's something that can return just one element at each iteration of the loop. Or in other words, this checks whether it can break this entire object into smaller pieces, giving us just one piece at a time, one element that we can work with on each next iteration, it can provide us with the next element from that object. This situation occurs here because this list of many elements can be broken down into individual elements and each of our numbers in this list is indeed such an individual element. So once this condition is met, I mean, this object is something that four loop is able to work with in the first place, then that four loop starts its work. I first selects the first element from our list, which is the number one and assigns it to our variable I. Because what we have here after this four statement, is a variable that we can name however we like. I happen to name it the single letter I just so I wouldn't have too much to write, but you can call it whatever you want. In this first so called iteration, which means the first repetition of this loop, we simply have I equals one, and now we can do something with that variable I. Simply just displayed it using the print I statement. Let me repeat. Let's not that this print I is indented and it's very important. This indentation happens that Python will know that this print function is considered to be inside of our four loop. Everything we do here like we print this variable, is the first iteration, the first repetition of our loop. This is the task we give Python to its instruction what Python has to do with this variable and we just print it. So that loop did what it was supposed to do, but then it goes back and checks if there are any other elements in this object. And if there are, this four loop will pull it out for us. And such an element exists, it's the number two. So now the loop assigns the value to our variable I and again, performs the operation or operations because you can have multiple operations. We have just one. It's a print function. It simply performs that operation for us. So it prints the variable I again, but this time, our variable has the value of two instead of one, as it did before. I displays two, it then goes back and checks one more time. If there is yet another element that can be pulled out and assigned to the variable that we called I, and it does it six times. After the sixth time, it again goes checks the object and it sees that all the elements from our list have already been used. So at this point, the loop has completed its task. But now let's take another look at our loop. Our entire list with those six elements can also be saved as a variable because we can write something like X equals then one, two, three, four, five, six, I press Enter. Now we can create the loop again. But this time, we will notice that we will have two variables. We can have four I in X, and now I press Enter once. Click cab to create indentation, and I print that I. First variable is that I that will be grabbing each individual element from our list, but the list itself is also a variable, and it's our second variable, which we call. So now press Enter, Enter, we can see that we get exactly the same result. But as I mentioned, inside this loop, we can also perform operations on each of these variables. I mean, it doesn't have to be one operation. It can be multiple operations, but let's create maybe a simple one. So I will write for I in X, Enter indentation with tab, and now what I will do, I will multiply our variable by itself. So it's I multiplied by I. Let's press Enter, enter, and now we can see that in the first iteration, when our element is one, I mean, our variable I has value of one, we get the result for one multiplied by one. Then next iteration, our variable will have value of two. So our displayed result will be for two multiplied by two, and we can see it repeats until we reach six multiplied by six, which is 36. And as I mentioned also, we can name that variable however we like. I was just lazy calling it I, but we can call it Marek, for example. Let's do four Marek in X. Enter. Now tab to make an indentation. But now I will print, I have to use my new variable name, which is Marek. I now multiply Marek by Marek. Press Enter twice, and again, we've got the same result. Let's press Control, maybe, let's clear that out. One more thing I wanted to mention is that the list is not only the type of data we can work with here. Another type of data that belongs to those iterable types, for example, is a string. We can write something like four I in. Hello, column, Enter, tab, print I. Now we can see that the loop can also break a string into individual characters and present each one separately in next iteration in the next repetition of the loop. But, I think at this stage, I think it should be enough to know about the four loops. So I will see you in the next video. Thank you. 8. Python break continue statements: Now I wanted to mention the so called break and continue statements. What are they and how they are useful to us? In previous video, we learned about the four loop and how it can iterate through the items in the list. So just recap. We can have a list of items one, two, three, four, five, six. I will save it in variable called X, and now I can do four I in X, print I. But let's say I want to find a specific number in my list, and maybe when I find that number, I want to announce it somehow and break all subsequent iterations. Or simply put, since I found what I was looking for, my loop has completed its task. That's exactly where the break statement is very useful. Let's write something like that. For I in X, create first indentation, I press tab one. I will write something like I I equals four, and I know we haven't talked about it yet, but this is basically how you can check if something is true or it's not. So here I'm checking if I is equal to four. But note, I have to press equals to twice. Yes. We will talk about it later. Now, I press Enter again, and I press tab twice. So what I mean, my indentation has to go even further. And now I say maybe print number four. Has been found. Press Enter, match the previous indentation, I press tab twice, and now I say break. Press Enter, and now I will create one indentation at the same level as the previous I statement. And now I say print I. Let's press Enter twice now. Now as we can see, this loop works normally for the first three elements. It displays one, two, and three. So my loop takes the first element, which is number one, assigns that value to my variable I, and it checks if I is equal to four. But because it has number one, it can see that it's not equal to four, hence it skips that more indented elements and goes straight to the line that is at the same indentation level, which means it simply prints element I. Which is one. Then it goes back to the beginning, pulling the next element from the list, which this time is the number two, and it repeats this process, checks if it's equal to four, and if it's not, then it will simply ignore those more indended lines. Goes through the loop again, it has three and then goes back and goes through the loop again until it pulls number four from the list. Now four becomes my variable I and it can see it does equal to four. Since this condition is met, it looks at what it must do in this case. I will check this time these more indented lines. It sees that this time, it has to display something different on the screen. It must show us the string number four has been found. And that's exactly what we can see here. But in the next line, it can see the break statement when the loop sees this command, it simply stops its operation. It simply knows that whatever had to be completed has been already completed and the loop is now terminated. That's how the break statement works. But there is yet another statement, and it's the continue statement. It's very similar to the break statement, except that the loop does not stop but continues until it completes all the iterations over all of the elements in the list. If we change that break to continue, let's write it again for A and X. I X equals four, everything the same. We say print, number four has been found, but this time, I will create two indentations and I will say continue. Print I and press Enter twice. And this time, we can see that for number four, instead of the number, it prints string number four has been found, but it does not interrupt its operation. The four loop keeps going. It checks all the elements in the list until it has gone through all of them. And sometimes it is useful if you, for example, have multiple items in your list with exactly the same value, and maybe you want to know how many you have them in that list. Every time the loop will encounter four, each time it will display that string instead of the number four. I mean, if we change our list to something like X equals one, two, three, four, five, four, two, four, let's run our loop again. We can see now it found all elements that have value of four. And I know that's for a short explanation, but at this stage, it will be all that we need to know regarding the break and continue statements. So thank you for watching. 9. 'while' loop: Previous materials, we saw how four loop works. We saw that four loop allows us to extract each single element from a more complex object like a list, and it allows us to perform some operation on each of these elements. For example, if I have ten elements in a list, then the loop will be executed ten times and that's it. However, there are rare situations where we do not have a strictly defined number of elements and we need a loop that will keep running until a certain condition is met. Trying to explain this in words usually doesn't make much sense. Let's do it through examples. Let's create something like this. Let me press Control L, and I will say X equals one. Our variable X is a simple integer. But now I say, while X is less than ten, Enter and create indentation with tab, print X. Now another line, indentation, X equals X plus one, and I will click Enter twice now. And we can already guess what that loop does. So initially, we have our variable assigned a value of one, and then we have our loop, our while loop. We say that while X is less than ten or perhaps as long as X is less than ten, execute all the instructions below, and the loop executes our instruction, which here simply displays current value of our variable. However, that last line might be a bit confusing. Someone might look at that and say, what it's supposed to mean? How can X equal X plus one? First of all, let's not think of it as mathematical task. Remember that X is our variable, and in the case of variables, it makes more sense to read this from right to left. But our variable starts here in the first line and we've got value of one assigned to it. But then we take that current value of variable X, which is one, and we add some other value to it. And here we are just adding another one. So we have two together. Now this new value, this integer two, it's now assigned again to variable X. X is now two. Our variable X now has a new value which is two and the L loop starts over again. And checks whether that new value of variable X is less than ten or not. Well, it's two, so it's less than ten, so the condition is not met. So the loop repeats again. The new value of variable X is passed to the print function, Python displays two this time, and so it goes until the value nine, as we can see. In this last round, let's call it that. The loop again checks if nine is less than ten, and it is less than ten, the condition is met, so the loop repeats again one more time. But this time it takes this nine, then we add one to it again. And we save this result as the new value for our variable X, which is now ten. Now when the L loop checks this new condition, it sees that this time the condition is not met because ten is not less than ten, but it's equal to ten. That means its work is now completed. The lo has executed actions on all elements that met the initial condition, but it is abandoned as soon as the condition is not met. It's also worth noting that the first X equals one has no influence on our loop at all, later on, because this is just initial value of our variable. But later during the execution of the loop itself, the loop repeats within itself. It doesn't go back to the first line. The loop starts at second line. What we recorded earlier as the initial value is only read during the first repetition of the but in every subsequent iteration, the last line sets a new value for our variable X, but the first one is no longer considered at all. But that well, we often see that last line written in Python in another way. Let's write something like this. Maybe X, this time will be, I don't know, 100. Now we say le X is less than 110, print X and then X plus equals one plus twice. If we look at this notation in the last line, it makes even less sense, but this is simply a shortened form of exactly what we wrote before, which is X equals X plus one, and we see if we run it now, basically the logic is exactly the same. For the time being, that's all we need to know about the i loop, so thank you for watching. 10. Python true false boolean: Python, as well as in other programming languages, we have something called a Boolean, and this boolean, in addition to its funny name, can have two values, and they are so called true and false values. And as always, let's take a better look at examples of what I'm talking about and how this boolean, be true or false can help us in Python programming. This time, you know what? Instead of doing it in interactive shell, let's maybe get out of it and exit function. Clear. And we will write and save it as a file now. We will create a file or use VIM, maybe Marek dot pi. That will be our program. And we can write something like X equals one. And now while X is less than ten, column enter, and you can see VIM creates the indentation for us. We don't have to press tab here, and I know by now, some of you might think, Mark, have you ever heard of that thing called IDE? Yes, yes, I heard about it, and don't worry, we'll talk about it, but we'll talk about it much later. For now VM is okay. So we've got that, and now we print X. And again, we do X equals X plus one. Or in previous video, we already so we could also write it as X plus equals one. It's basically the same thing. Let me save it to save in VM IpresEscape, column WQ, and now I can run my program. I run it by typing Python three, mac dot py. Now we have something that we've seen before and the result that we expected. But what if I change that initial value of our variable to ten or more? Let's open the file again. So what I'm saying, the first line, let's change it to 20. I say X equals 20, and then the first iteration will be while X is less than ten, but X is 20 and 20 is not less than ten. It's more than ten. But let's see what happens. I press Escape, Colm WQ to save that new program. I can also cut it. We can see our program. Let's run it. I press Enter and we run our program, but nothing is displayed. Why? That's because in that very first line, we set our variable to hold value of 20, and then the loop checks on the first iteration whether this condition is met, if X is less than ten. I 20 is less than ten, no, it's not. Since 20 is not less than ten, the condition is not met. That means the loop gets this bull value of false. So it doesn't execute even one repetition, not even one iteration. Simply already on that first line of Wil loop, this loop is abandoned. However, there are situations when we want the loop to execute at least one repetition. And to do this, we need to change our program slightly. So let's rewrite the first line first line of the Willoop I mean. And now I say While through, and I leave that print X. I will do further checks below. All right, so what I'm saying here is I forced now the loop to perform at least one repetition because we told it, you have nothing to check here. The condition is already met. I'm saying you while true. So there's nothing to check. I'm saying you that the condition is already met. Doesn't matter what it is. And first iteration must be executed. Therefore, the loop, whether it wants it or executes everything what's below, and it reaches the first line where we have our condition, but I changed it slightly. It checks now if X is greater or equal to ten, and in this case, it is 20 is greater than ten. So the loop will execute whatever is in even more indented lines. It will print that number is too large and below, we can see the break statement that we saw in the previous videos. So we know that this loop will simply be abandoned at this stage. But maybe let's see how it works. I will run it. We forced that first iteration. We can see it was printed, the 20 was printed because we forced that first iteration. But now let's change that initial value of X to something smaller. Maybe let's clear that. Let's VM Marek. Now let's say X equals maybe one. What it should do now, it still has that first iteration forced, but because this condition will not be met initially, these two lines will be omitted. These two lines are only considered if the previous condition is met. But one, for example, one, one is not larger or equal to t. I will repeat the process of X of increasing the value of the variable X until it reaches that. Well, maybe let's run it, should be easier. Python three, Mark Pi. What is important here if we force this bullion for the Wile loop, we have to break the program somewhere else because otherwise it will run forever and we break it here. So even though we force the first iteration, we don't have to worry much about it because we break it somewhere else. But what happens if I didn't have that break statement here? Let's have a look. If I remove it, now we basically have nothing that would stop this Wil loop. So let's save it. Let's run it. And now we see the number is too large, but it doesn't really matter because there is no single line that would force this wile loop to stop. There is no break statement. Let's Control C, maybe. So I have to stop it like that using Control C. You can see it counted already to over 3 million. So that's basically it. That's what bullion true and false are, and this is how I can use this bullion to force iteration for the Wil loop. I hope that makes sense. As always, I recommend not only watching this material, but also experimenting on your own to fully understand how it works. Thank you for watching. 11. Python f-string: In this video, I wanted to talk about something called F string. As usual, I won't try to explain it in words. Let's get straight to the examples to see what it is and why it exists in Python. Let's say I have a variable. Let's call it X, and the value will be string mac. What I can do now, I can run print. I can say hi, maybe I will add spice and then plus X. And if I run it now, we can see that Python adds those two strings together. So the first string is high, and we know it's string because we've got it in quotes and Python knows that this is string data type, and the second string is Mek. But that second string Mrek is read from the current value of the variable X, though, which means Python looks at that X and says, Uh huh. The second part is not in quotes, so it must be some variable then. I must find that variable and check what is currently recorded in that variable called X, once Python finds it, only then it displays the result. It's worth to note that when it finds the variable X, it checks also its data type. Since Mac is in quotes, it knows it's a string data type, and ultimately, Python displays that high mark. This whole operation, when we add one string to another, is called string concatenation, and we have done such operations before, so it's nothing new for us. But let's do something different now. Let's type height equals 178, it's in centimeters and weight equals 93.5, and it's in kilograms. But that doesn't really matter. And what I'll try to do now, I will try to use that string concatenation method. So I print So you've got print, your height is in quotes, as it's string, I will try to add that height variable, and then I add another string and your weight is, and I will try to add that weight variable. Let's click Enter. As we can see, Python is complaining, and it even tells us exactly what it doesn't like. It says, You can only concatenate string to string, not to integer. This makes sense because even this entire operation is called string concatenation, which means adding some strings together. Here, what is the first value we try to provide? What is the first variable? I mean? Well, it's an integer. It's the whole number 178. In the second case, we've got floating point number. I can tell you right away that it would also complain about it because it's floating point number and not a string, but because Python encountered that integer first, the error only mentions that integer. We simply cannot add those two data types together. Theoretically, we can fix this in various ways. For example, we can write our values as strings by simply adding quotes around them. My height because this and my weight becomes this. And if I try to run it again, now it works fine. Since your height is 178 and your weight is 93.5. That's because we changed the data type for height and weight. But the thing is, what if we want to keep our variables as previous data types? I want to have that integer and floating point number. I don't want to keep them as strings. So let me convert them back. And the other option we have, we can use STR function, which can change the data type of current variable to a string regardless of what data type it currently is. So I've got my variables back to what they were integer and floating point, and now my print will look a little bit different. I will change this height to string using STR function. And because it's function, we use those brackets, and then I go to weight and I convert weight also to string using STR. Function. Let's run it now. As we can see now it works again, even though the variables are kept as integer and floating point number. We only change them once for that print function, but it doesn't change the data type of the variable itself. You could say, Hey, it works. Yes. Yes, it does work, but it's a bit tedious process, isn't it? We have to look for all those variables, check which ones aren't strings and use some functions to convert them to strings if they aren't. This really isn't that clean, is it? So there is another function, sorry, it's a convenience feature, I would say that was added, and it's called F string. And I believe that F string comes from the format string because the syntax is similar to that format string method in the Python versions. So how do we create that F string? We simply I will use up arrow again. So this is our last print function. And now, will just move it to the very beginning and I add little F. And now I don't have to change any data types with function. Python will do it for us automatically if I just enclose those variables in so called curly brackets. This is my first variable I want to convert. I use curly brackets here and the second one is the weight. And now I also don't need these quotation marks. Because Python will convert those values to string first, so it will be a very long string of characters. I have to add quotation mark at the end because otherwise, all of that is simply one long string. Now, if I presenter, then you can see that I did something very stupid because I can also get rid of that plus. That's better. But now look at this syntax and look at that syntax. I think this one looks so much better. In fact, you'll encounter F strings very frequently because also this process called string concatenation is used very often, I would say in Python. That's all I wanted to say about F strings. It's essentially just a convenience, but it is very important and it's commonly used feature in Python. Thank you for watching. 12. Input function: Now let's talk about the user input or the input function. What is it? User input is a function that allows the user of our Python program to enter some data. Let's take a look on how we use this function. This is what we did in previous lesson regarding the F string. But I will copy that. That might be useful, let me just exit. Maybe we will write a little program this time. A little VIM, and we'll call it Mac dot pie. Ah, okay, I already have Marc dot py program. Never mind. We can reuse it. We just delete everything here. I will paste that line and I will add that height. That was in centimeters and the weight that was in kilograms. This is our program, so I will escape column WQ. I will save it. And if I run it now, we have exactly what we had before. Python displayed what we had already seen in previous video. But what if our user wants to enter their individual data themselves? Because every user will have different height and different weight. Don't want to have those static entries in the program. We want a user to be able to type in the values for the variables. Plus, we need to have some accessible way to input those variables when running the program because our users probably don't know Python. For us, it's not a problem. I can open the file, change the variable. That's because we know Python, but our user probably doesn't. The input function is used for exactly that. Let's edit our program again. Then we'll go to Mark Pi and what I want to do. Is to use input function. Because it's function, we use those brackets, and in fact, I don't have to put anything in those brackets, but that's a bad idea because what I can do, I can put some hints for the user about what to enter. And for the height variable, the user should enter the height is and preferably in centimeters. So I can say as a string quotes, I can say here, what is your height in centimeters? And for the weight, I also use input function in quotes again, and I can ask user, what is your weight in kilograms? And once the user types that in, that user input will be then saved as our variable for height and for weight. So now let's save it with c colon WQ, and they run the program again. And we can see that program encounters that first user input function. So the program stops and waits until that input data is received. So my height is, let's change it maybe 150, I say, just to put something different. Now it asks me for weight, maybe 88. If I press Enter, now our program has all the variables it needs, so it displays your height is 150 and your weight is 88. If I run the program again, maybe different user runs it and they have different height and weight, maybe 201 hundred, the result will be displayed for these new variables or for the values kept in those new variables. As always, I recommend not only watching this, but start playing around with those functions simply to remember them and understand them better. Thank you for watching. 13. Python Functions: In this material, I wanted to talk about functions in Python. In fact, we have already encountered several functions. Probably the most popular function that we used almost every time was the print function. We can do something like print hello world, and this is so called built in function, meaning that print function is immediately available in Python, and we can access it right after installing the Python itself. There are many built in functions. For example, the other one is length, and we just type LN N and it shows us the length of a given object. For example, I can do maybe a list. 56789. I press Enter, and we get the length of that list that was passed to the LN function. We can also check the length of the string. It's not a problem if I type length hello world. It will give us 11 because that space is also included. It is a special character that is part of this string. One more function I wanted to mention is the help function. It displays very helpful information for us. It's called help, so no surprise. For example, help n. It will show us more information about that length function. Let's press Enter, and we can see that length function is indeed a built in function, meaning it is immediately available in Python. It's installed together with Python. Press Q, and we can do, well, maybe the same for print function. We can also see that print is built in function. Help will also show us what we can put inside those brackets. Q again to exit. That's fine, but what if we want to create our own function? In fact, it's pretty easy, let me show you how to do it. Let's maybe exit that and clear. We had a little program in previous video. It was that one regarding user input. So maybe let's change this one. Maybe let's change this program. I will say VIM Mark D pi, and now maybe I want this print, which is here, maybe I want it to be in the form of a function. So we can do something like that. I can define my function. So I type DEF to define my function. Then I choose a name for my function, whatever it doesn't really matter. I will call it maybe F one because I'm lazy and I don't want to write too much. And after that, we type parentheses. That's because each function will have to have those parentheses, and in fact, inside them, I can also add some parameters. We can see here inside that input function, we can add that string. We can give the extra information for our user in the form of a string. That's how you define what can be actually included inside those parentheses. But for the time being, maybe I will just leave them empty. We will have no parameters. And now after that, I just need col. If I press Enter, you can see that a VM adds that indentation automatically because whatever I want to have in my function has to be indented. They want that print function to be part of my function. Well, in fact, that will be my entire function for now. So that's it. Believe me or not, but this is our function. Let's save this program now. I press Escape, call on WQ. And let's run this program. I say, Bin three Mark Pi. It asks me my height 17 night, 93.5. We can see it looks like it doesn't do anything, and that's because we've got the function defined, but we haven't run. I go back to my program Mark Dupi, this is how we define function, but we never said to run it. What I can do, I can just type new line here saying F one. That's how I run my function, or you can sometimes say I call my function. I want my program to run the function that I've just defined. Let's save it. And let's run it again. I have to type again the variables 17,893.5. And now the function was not only defined, but it was also run for me. All right. But since we have already the user's height and weight, let me open the file again. Once we got that data from the user, we can calculate their BMI. And the BMI, the body mass index, I mean, simply tells us whether our body mass in relation to our height is appropriate or not. Or in other words, whether we are overweight, underweight, or maybe everything is okay. So let's first maybe Google how to calculate the BMI. So we can see we have to divide the weight in kilograms by height in meters squared. So for example, a weight of 73 kilograms and height of 1.7 meters. Our user gives us the height in centimeters, remember, though. But then it's not only the meters, it has to be meters squared. Maybe somewhere it's shown better way like here. We can see it's weight in kilograms divided by height in meters, and then whatever it is, we will have to multiply it by itself because it's squared, or maybe this is even better. That's what it looks like. All right, let's do it then. And we've got our F one function, it's fine. We can leave it. Let's define next function, which we should call probably BMI, I guess. And then the column enter, and we can start defining what it should do. There is also one more thing I didn't talk about. It's regarding that input function. The fact is that input function, whatever we put here, it will be saved as a string. So height currently will have value of our height in centimeters, but it will be kept as a datatype string. So we also have to format both of them to either integers or floats. So maybe I will define new variable height in meters float. Oh, that looks terrible, but never mind. What I have to do I have to take my current value for height. So I take the variable height that we already have and store. I run a function called float. This will transform whatever is currently there in that variable height, it will transform it to a floating point number. In fact, the same way I can use STR, remember, the string, but it's already string, and I could also use INT to create an integer out of that. But let's stick to float because maybe somebody wants to be super precise and perhaps input something like I don't know, 178.4 for some reason. I want to grab all that data, but I have to store it as floating point number then. But then one more thing, remember, we are not interested in centimeters. The value we have to provide is in meters. So let me also divide it by 100. If somebody gives me 17 8 centimeters as the value, I will create 1.78 meters. That's exactly what we need for our calculation. Okay, I think that's it. Now the weight. In fact, the weight doesn't have to be we just have to change the data type, and we can change it. Well, let's call it differently first of all, float equals float. Well, we have to take the current variable weight and just change it to float. We will use, again, function float. So we have two new variables. It's height and it's in meters because we divide it by 100 and it's floating point number because we use function float. But for the weight, we only change the value to float. W. Alright. Next line, we will just calculate that BMI. BMI equals, we have to take that. We have to take our weight, but as a floating point number. And now we have to divide it by our height in meters. That's our variable for that, but not only that, it has to be squared. Remember, we have to multiply it by itself and we will have to add those brackets in that case. Means we grab our weight and we divide it by height in meters squared. But now, it would be useful to also print the value as the output for our user. So we will add that print function again and we can use the F string that we already know and we say your BMI is in curly brackets BMI. We just want to display value of this variable. Okay. And last but not least, we not only have to define our function, we also have to call it. We have to run that function. So we say BMI and just the brackets. We can leave the F one as well. We will run F one function, and then we will run the BMI function. Let's save it, escape column WQ. And run our program height one ****, weight is 93.5 kilograms and the program says, You BMI is 29.5. There's actually one more thing I want to mention. Let's go back to our program, maybe even two things. First of all, the function, we create it once, but we can call it several times in our program. What I mean, if I run now BMI that, BMI, that, I can call it several times. Let's run it again. 17,993.5, you can see that function run three times this time. Maybe let's clear it and go again to our program. The other thing I wanted to say is that the function has to be defined first before you call it, before you run it. Let me show you what I mean. Let's maybe remove those two lines and maybe I want to run a function, BMI here already. Let's see now what happens. 17,893.5. Python says name BMI is not defined, which is not really true because it is defined, but the problem is Python is interpreted language, it's called, which means it will take every single line and run it as it is one by one. It checks the weight, it checks the height. It then check the function and it can see, but that function at this stage is not yet defined, it says, sorry, the function is not defined. Whereas if it would go any further, it would sit there, but because it's interpreted, it doesn't do that. That's very important to define all your functions first and only then run it. It's a little bit longer video, but I hope it's useful. Thank you for watching. 14. if, elif and else: In this material, I want to talk about something called IF and sets, conditional statements, they're called. These conditional statements are used to check whether a certain condition is met in a program or not. Maybe let's move to some examples right away because they are the easiest way to explain what it is all about. I will create a program, let's call it ILPi I will say X. Equals input, the user input. We already know what it is, and we say enter the value of variable X. We remember from the material about the input function that when the user enters anything here, it will be saved as a string. So we need to convert it to either an integer or float, and I will change it to floating point number. So I will use function float. Okay. And now I say if X is less than five column, then print X is less than five. Now, what I can say is a leaf, which means plus I, it's si, but we say a leaf. I say X is less or equal ten. I will say, then print that X is 5-10. How do I know that? Because Python, as we know, will go from the top down. So it checks first if X is less than five. And if it was, the program would stop already here because the condition would be met and it would be printed that X is less than five, indeed. But if that condition was not met, the Python will go further and we'll come across this statement. So we know already that our X at this stage, if we arrived here, we already know that X is not less than five. But we maybe want to check if it's somewhere 5-10, and that's how we can check it. We already know that it's five or more, so we just want to know if it's less or equal than ten. It must be if it is, it must be 5-10. And now I can create another Alif. I can create as many of them as I want. Maybe I want to check if it's also less or equal 20. But you know what? At this point, maybe I'm done, and I just want to say, let's call it LS, and I just use LS. That means for anything else. Well, at this stage, I know that X has to be greater than ten because I know it's not smaller than five. I know it's not somewhere 5-10, so I can be pretty confident that it has to be greater than ten. So I can say, print, X is greater than ten. Let's check if it works as we expect it. Say Python three. If else it asks me what I want to set for my variable, I will say three and indeed, three is less than five. If I run it again, maybe for value ten, it is correct. It says X is 5-10. If I do maybe 20, it says X is greater than ten. But now, remember in previous episode about functions. We created a function that calculates our BMI and the file should be still here, a reminder, the BMI was a body mass index, and it's an indicator that tells us whether our weight is in relation to our height. If it's within the norm or if it's rather outside of that norm. We save that file and we can now modify it a little bit using that IL statements to see to check if our BMI is fine or if it's not fine. Let me clear that and maybe just as a reminder how it worked. I type in my height in centimeters, my weight, and it says, my BMI is 29.5. But is it good, what is it? Let's check first, what is a healthy BMI? What is the norm? I? Alright, so we can see that under 18.5 score is described as underweight. 18.5 to 24.9 is healthy and 25-29 0.9 is overweight. Then we have also obesity and severe obesity. Let's use it. Maybe I will put it here so we can see it. And let's amend our program now. I'll say VM Marek, y we can leave everything as it is. We will just go to our BMI function. And now, once the BMI is calculated, I can use it in the program to check if that BMI is for a healthy person or if it's not. So first, I say, I BMI is below what? 18.5. That's our starting point. So I'm checking. If my BMI is below 18.5, that means I can use that print statement, maybe. You can see that indentation is created here automatically for me, and I print your BMI is BMI. The result, whatever is under 18.5, if it's 15, 16, then that means you are underweight. And now maybe let me copy that because that will be just too much writing. I will yank two lines and I will paste paste, paste maybe again. I think that's okay. That's my first check. In next check, if the Python program reached this point, that means my BMI is not below 18.5. It must be above it. So now I will check if it's between 18.5 and 24.9. Well, in fact, next threshold is 25 starts from 25. So I can also say here, just if it's less than 25. I believe that's what they mean, 24.9 9999, you know what I mean? It has to be simply below 25. So that's exactly what I need, and that would mean I am in healthy range. You are in healthy range. Or maybe simply you are healthy. Now, next one goes up to 30 because it again says 29.9, but it means to be below 30 simply. So I say below 30, you are overweight. Okay, well, that's enough. I will say just L. But these two, they are not if statements, yes. They are a leaf. You can have only one I and one L. Everything in between is a leaf, if, and we will just change this. It's not overweight, it's obese now. It's either obesity or severe obesity, anything above. So let's check how it works, if it works at all. So I run Fon three macular pi, asks me about my hive once over night. My weight is 93.5. And now I can see that my BMI is 29.5, but I can also see that I'm overweight. So if we check that program, it said that I'm overweight. That means I checked if my BMI is below 18.5. No, it's not because it's 29.5. So we checked the second statement. If it's below 25, no, it's still not, and I'm just below 30, 29.5. That means I'm still in this category. But if I run the program again for, let's say, maybe I'm 180 and I weigh 50 kilograms. That means my BMI is 15.4 and I'm underweight. Okay, hope that makes sense. Thank you for watching. 15. Classes: In this material, we will talk about so called classes in Python. And in fact, we have been working with classes almost all the time. We use them in every previous episode, but it might not be so visible or obvious. Let's take the simplest example. I will write something like X equals one. And we now print that X. We simply take the value of one and we assign it to our variable X. And with the print function, we simply display it on the screen, and we already know that this one is a data type called integer, meaning it's a whole number. But how does Python know that this is an integer? And how does it know what can be done and what cannot be done with that integer? Remember the type function that shows us the data type. Let's use it here. As we can see the integer that is a whole number is a class. That's the very class we are talking about, and that variable X or that number one are so called objects. So that value one is an object that belongs to the integer class, and I can create unlimited number of such objects. For example, I can create another object. Let's call it Y, yes. Y equals two. Now if I run same but for Y, this is my second object, but it still belongs to the same class, which is the integer class. Some of you may have heard that Python is referred to as an object oriented programming language, that indeed is the case because when working with Python, we are practically always working with some type of objects, whether we realize it or not. If we write something like that, X equals hello world. If we now print type for X again, now we can see that hello world was assigned to variable X and it now belongs to a class called string. That is a sequence of characters. But what does it really mean? It means that the string class will have different characteristics. For example, if an object is in string class, we cannot multiply it by floating point number. Whereas if an object is in the integer class, we can multiply it by both another whole number or by floating point number. So all these rules about what can or cannot be done with a given object are recorded in the class in which that object resides. And at this stage, to explain this even in more detail, it might be the best for us to create our own class as well as object for that class, or even we will create several objects within that new class that we are going to just as we can create numbers or strings, maybe we want to create a new class to create, I don't know, rectangles. So yes, let's say we want to create a class for our rectangles in Python. So how do we create such a new class? Maybe let's start from creating a new file. I will use VIM, I will create maybe Me class dot pi. Now what I have to do, I just write class, rectangle or whatever I want to call it, my new class and I add column at the end. I've just created my new class as press Enter. Now we can create what's called a properties for our class, properties and attributes, actually. What I mean, as we know, every rectangle has a length and a width, yes. So we can define those our attributes for our rectangle class. And to do that, we need a special function called Dunder in. I know it sounds funny, but it has this unusual naming because it is written as underscore underscore, then in it, and then again, underscore underscore. And this Dunder in it is a special function that is automatically called by Python every time we create a new object from this class, which we will do shortly. Then we also add brackets, and in these brackets, we provide so called parameters. And currently, the only parameter we will have here it's called self. I mean, we can call it whatever we want, but we'll discuss it shortly. Parameter will later be replaced by the name of the object we create from this class. I know it's getting complicated. Don't worry about it. We'll go through it. Same with the self. Don't worry about it. It will be explained shortly. For now, let's write the rest of the things we have to write, okay? We need those attributes for our object, which are length and width because that's what each rectangle has. So let's finish our function first. We have to just use depth because each function we write we define by using that DEF, yes. I keep saying function but somebody to make it even more difficult, said that if you write a function inside the class, it's called method. But never mind, it's really not most important thing here. We have to finish it with column or function plus Enter. Now we are defining the attributes, length and width. So we say self width, and maybe it's ten and centimeters, let's say, leave ten and self length it's maybe hard coded it to 20. So width of our rectangle is ten, length is 20. And now to understand the self what it is, let's create our first object from that rectangle class. Maybe maybe to make it super clear, I will do something like that. We finished playing with our class, we now start with our object. And the object, how do I do that? How do I create an object? I can create, for example, my first rectangle, rectangle one, and I just say equals to rectangle, and I use brackets. And also note, that's what we usually do. For class, the first letter is usually capital letter. For objects, it doesn't really matter, but none of it matters. It's just you can create a class that starts with lowercase. It's just simply something that software engineers agreed on. That class should start with capital letter, and then the remaining ones are small letters. That's how you create your first object from that class. What I can do now, I can print my object rectangle one. I will press Escape column W. I will write it to the file and maybe I will open another terminal, I will open it here. And I will run that program to see what happens. I mean, first, let's check if here is where my file is ASL. So we've got previous Mark Pi, but now I've just created Mark class, so let's run. When we run our program like that, what Python will display is the memory location where it created this new object that we called Rectangle one. All of this, you can see, is simply a memory location where Python saved that new object. But what really happens here is Python will read that rectangle one and the first parameter we placed here, which we called self. Remember, we store parameters here in those brackets. First parameters self, Python will replace that self with rectangle one. I will place rectangle one here, and then it will replace also these with that value, rectangle one. Rectangle one width is ten, and rectangle one length is 20, and we can actually retract that data. I mean, we can say here in our program, we can say also print rectangle one width and the same way, I can get value for rectangle one length. Again, for this object rectangle one, I place this value in our class here, the self becomes rectangle one. Now I've got rectangle one width, rectangle one length. I will say escape column W. We will write it to the file and I will run the program again. Now I extracted those values. These are these attributes. Rectangle one width is first attribute, and rectangle one length is the second attribute of my rectangle. I just want to show you something to make it clear. This self, we called itself, but I can actually call it anything I want. If I want to call it Marek, I can do, but then I have to replace those also with Marek. If I write it to the file again, escape Column W, if I run the program again, as we can see, it still works fine. But for the Dunder in it function, it was agreed that, for the Dunder in it, we will use self. Simply, if you open the program, you will know immediately what it is about. I will change it back to stick to those rules. But anyways, someone might ask, Mark, but the point of this because it looks like some unnecessary notation. And as long as we have only one object, it might actually seem that way. I agree. However, remember that we can create the class only once, and then we can create an infinite number of objects from that class. So now let's create the second object and we will call it rectangle two. So maybe escape, we will yank it Yang five Yang. I copied that, I will just change to rectangle two. I'll change it here, and then I want to print the values for Rectangle two this time. Now we created second object. And when Python starts reading the program, it will see rectangle one first. And then it will see that we want to create an object from a class that we call rectangle. So it will find this class. I will replace whatever we put in parameter here. And as I said, you will usually see a word self here. It will replace that self with rectangle one, and it will use that name for all remaining attributes. So we have rectangle one with is ten and rectangle one length is 20. Then it will print all those values. It will see the second object rectangle two this time. So it will go back because we can see. I mean, Python will see that we want to create objects from the same class. So goes back, replace this self with Rectangle two this time, and all the attributes will be called rectangle two width and rectangle two length. And that's what we want to read here. So if I now write to the file as cape column W, and we run our program, what we first can see that the second object for rectangle two has indeed different place in memory. It's separate object created somewhere else in memory. I can see only two last values have changed, but anyway, this is new location. This is new memory location for object two that we've just created. But now someone might be looking at that and say, Mark, this completely doesn't make sense. Why would I create more objects when they are all exactly the same? Well, each of these rectangles has a length of 20 and width of ten. What's the point? Again, indeed, at this moment, that's true. These objects don't have much meaning because our length and width are hard coded in our class. We hard coded those values here. However, this doesn't have to be the case. We can modify our class now so that it can accept any values for the length and any values for the width. And to do this, we can add additional parameters to our special Dunder init function. And when I say parameters, I mean here, whatever we have in these brackets, because here is where we store parameters. Once again, it doesn't matter what we name them, but to make sense, we will name these parameters width and length. Or maybe I will add R rectangle width. I just want to distinguish it from this, so it's clearer what is what. Then I will add R length, and now I will no longer want to hard code these values. I just want to read them from whatever program or user provides. I'll use Rwidth and guess R length. But what it means now, now when we build our next object, so I will go here where we start building our object, I will need three parameters and the first one remains unchanged and it's self, and it's something I don't have to provide within brackets because self is simply the name of my object. We already know that rectangle goes and replaces that self. But I have to provide second and third parameter for our object. So maybe I say, I want to have it like ten in width. This will be my width. And second one, after comma, we separate them with commas. I say 20. But my second rectangle will be different. Maybe it will be 5,100. It will be much bigger. Now let's save it, column W, and now I run the program again. Maybe let's clear it and run the program. Now what we have you can see that Python stores these objects still in the same memory location, but now each object has different attributes, just to make it more confusing. These what we provide here, ten and 20, for example, these are called arguments. These arguments we provide here become parameters when they are read by the class. Okay? So this argument ten becomes parameter called R width, and then that parameter R width is used here as a value for attribute self width. Loads and loads of names, I know. But the most important is to understand the concept, not remember all those names. But I just mentioned it just in case you are interested in. Also remember this I keep referring to as function. But if we write a function within a class, now we really should call it method, not function, even though it's function, but I don't know, somebody likes to make it complicated more than it should be. But never mind. But we've got width and length, yes. So maybe we could add additional features for our class and we can calculate perimeter and arar. Let's go back to our class and we want to define perimeter. And area, and we define them as a separate functions for our class. So I say define function called perimeter and we read the name of the object again. So for rectangle one, we will change again this parameter to rectangle one because it will have to rewrite that value for every single object. My second function will be for area. I will define area as well and also add the self parameter. So let's start writing this function. We will say print F. We know F strings already and we say perimeter. Is we have to calculate by multiplying width and length, which in our case is self width attribute, multiplied by self length. Attribute. So again, because that might not be perfectly clear. I create first object called rectangle one. I created from rectangle class. My first parameter itself is the name of the object itself. Now I pass first value, which becomes parameter R width that R width now becomes rectangle one width. And because this function also replaces that self with rectangle one, it will read that rectangle one width and will multiply it by rectangle one length. Hope that makes sense. And for the area, we print Area is just realized. They're probably just watching and saying, like, Mark, what are you doing? Of course, this is area because that's for the area, and this is perimeter. Never mind. Be perimeter, how we calculate perimeter, we do self width. We add self length, and we multiply it by two. But we have to put brackets here to make sure this operation is done first. That's better, isn't it? All right, so that was a little hiccup. But now I can go to my object and maybe let's remove these lines. We will no longer need them. And now I will say rectangle one, Area, and I will also say rectangle perimeter. First thing, somebody might say, where is your print statement? Well, note that the print I used already within the class. So we don't have to print now. It's already a part of our class O the method that we wrote, we call that method function, but it's method within class, we call it area and that's what it does for us. It not only makes that operation, it also prints the output of that operation. What I'm really saying in this line is that I'm interested in object rectangle one, which is this one, which is created from class rectangle with these parameters, but I'm only interested in a function within that class that is called area or method that is called area, yes. So I will only display this portion. But in second line, I'm saying, You know what? I'm also interested in perimeter. So I will also run this method within that class. Let's do the same for rectangle two. All right. Let's write it to the file, Escape, column W, and let's see what happens if I run now this program. Okay, it moans something about line seven. So it's one, two, three, four, five, six, seven, and of course, it does because I'm stupid. Do you know what it is? You got a missing bit. It's very important as you can see. It's the column here and there. And maybe let's remove this line. Or no, maybe let's add extra one might look a little bit better. Okay, again, escape, colon W, let's run it again. Now it's better. It says Area is 200, perimeter is 60. For first object and for second object, it says Area 5,000 perimeter 300. And you know what? That's cool, but the thing is you don't normally do it like that where you write your class and your objects in the same file. You usually have your class in one file and objects are created somewhere else, usually as part of your program. So let's see how it can be done, how it can be split. I'm saying create new file, Marc object. Mark object, it will be called dot pi. And now I will copy my object. To this file. Perfect. Well, I don't need it, in fact, here, so DN and D. Okay. Now it's removed. I will write this file. This is my Mark class file, and here is my Mark object. However, I have to add one more thing because this object has to know where that class is. So I'm telling it by using import Mark class. Those files are in the same folder, so I just have to specify the name of my file and I can ignore the dot pi extension. Just provide the name of the file. That's it. And in this case, it will be fine. But I just wanted to mention one more thing. We've got class rectangle, yes, but maybe I want to write more classes like a circle, like a square, whatever triangle. But here in my program, I'm only interested in class rectangle. I'm not interested in class triangle, for example, right? So I can be more specific here. I'm saying here from Mark class. Import and which class I want to import. I only want to import rectangle. That's what I'm interested in. So if I had multiple classes, I would only pull the rectangle one. All right, let's save it now. And now, what I run it's not Marc class, but Mark object. Let's run it and we can see it still works fine. I know, it's very long lesson, and you know what? It's very difficult to understand. Don't worry about it. Even if you watch entire video and you're still looking at that and you're like, Mark, what the heck? This is so overcomplicated. I don't know, whatever you might be thinking. I want to tell you, don't worry. This is really one of the most difficult subjects in programming generally, not only Python programming, but generally in programming because there is so many moving parts, so many different names like those attributes, parameters, blah, blah. It's very easy to get confused with all of that. And I get you. And you don't even want to know how long it took me to understand it. And I say I understand it, but sometimes I still struggle till now. So especially in the program when you pull multiple classes and the multiple methods that blah, blah, you know, it's so easy to create that mess that is difficult to unravel. But never mind, I hope that anyways, this video is useful and I hope that does make sense. So thank you for watching. 16. Python IDE - PyCharm vs VSCode: Let's talk about IDE now. IDE stands for integrated development environment, and the most popular ID for Python is called Pycharm. But Pycharm is a Python specific tool. So if you want to work with more than one programming language, you might want to use VS code instead, which allows you to install extensions for any programming language you wish to use. It also has extensions for bar scripting, answerable, yaml files, et cetera. VS code is very good and it's something that I use and I can recommend. Generally, an IDE is simply an application that helps you write, debug and test your programs. It has some cool features like auto completion, but I guess many of you are wondering why we haven't used one at all in this training. The reason is a little bit personal, I would say. When I first started learning Python, every single course or training began with IDE. You had to go through several lessons installing and configuring that ID and it embedded in my mind that an IDE is necessary to even start working with Python. Took me quite a while to figure out that it's completely optional tool. It's something you can use, but it's not a requirement. I mean, you will probably end up using one ID or another because it can really help you, especially when your programs become longer and more complicated. However, I don't want you to start your journey with that feeling that it's the first thing you need to know when learning about Python. Can see, we completed this entire course without an ID, and it didn't even feel like we are missing something here. So have a look at PyCharm and VS code, or maybe you'll find it another one that you like best. They're all very easy to install. Think of them as a notepad on steroids. They will make your programming more convenient, but I will let you explore them yourself, as it should be your choice, which one you want to work with. So that's all really about the ID. That's all I wanted to say. Have a look at them, choose one. It's not that important, really. It's just a convenience tool. So thank you for watching. 17. Further learning: Congratulations on completing this Python programming course. You now possess all the essential knowledge and skills to start your proper programming journey. If you are interested in Dobs and Cloud technologies, then please remember that you can join our community on automation avenue.com platform where you can learn all about Terraform, AWS, Cloud, Python, and many more Cloud and DobsRlated topics. I hope that helps and thank you for watching. Mark.