Made the first calculator project. I tried to add in some notes just to clarify some things for myself. Maybe this will help other people as well.
I also made it so when you type "Reset" the calculator resets itself.

Here's the code if it helps.

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import re

print("Our Magical Calculator")
print("Type 'Quit' to exit\nType 'Reset' to reset")
previous = 0
run = True

def performMath():
    # when changing var in function, established outside of function, use global
    global run
    global previous

    if previous == 0:
        equation = input("Enter equation:")
    else:
        # prints the previous sum and asks for new input
        equation = input(str(previous))

    if equation == "Quit":
        print("Goodbye!")
        run = False
    elif equation == "Reset":
        previous = 0
    else:
        # using regex library to eliminate certain characters as input
        equation = re.sub('[a-zA-Z:()=_{}?><" "]', '', equation)

        if previous == 0:
            # evaluating the equation (str)
            previous = eval(equation)
        else:
            # evaluating the equation + the previous answer (str)
            previous = eval(str(previous) + equation)

while run:    # ( == True)
    performMath()