Calculator on Python

I'm just starting to learn python, and recently I tried to create my own kinda calculator. I wrote the code, and everything looks pretty fine to me, but for some reason I get the error 'if math_multiply: NameError: name 'math_multiply' is not defined'. I get it whenever I try to do anything, but multiplying. Please help me with this. Attaching code to the message as well.

P.S.: I know this question is very stupid, but I am a newbie who's only starting... So, please pardon me.

f_n = input('Type in your first number: ')
s_n = input('Type in your second number: ')
math = input('What are we doing? ')

if math == '*':
    math_multiply = True
if math == '+':
    math_plus = True
elif math == '-':
    math_minus = True
elif math == '/':
    math_divide = True

if math_multiply:
    print(f'Your answer is: {int(f_n) * int(s_n)}')
elif math_plus:
    print(f'Your answer is: {int(f_n) + int(s_n)}')
elif math_minus:
    print(f'Your answer is: {int(f_n) - int(s_n)}')
elif math_divide:
    print(f'Your answer is: {int(f_n) / int(s_n)}')
else:
    print("It's not an arithmetic operation")

Solution

You only set math_multiply if they entered *, it's not set if they chose a different operation, so you get an error when you check its value. You should initialize all those variables to False so that the later tests will work.

f_n = input('Type in your first number: ')
s_n = input('Type in your second number: ')
math = input('What are we doing? ')

math_multiply = math_plus = math_minus = math_divide = False

if math == '*':
    math_multiply = True
elif math == '+':
    math_plus = True
elif math == '-':
    math_minus = True
elif math == '/':
    math_divide = True

if math_multiply:
    print(f'Your answer is: {int(f_n) * int(s_n)}')
elif math_plus:
    print(f'Your answer is: {int(f_n) + int(s_n)}')
elif math_minus:
    print(f'Your answer is: {int(f_n) - int(s_n)}')
elif math_divide:
    print(f'Your answer is: {int(f_n) / int(s_n)}')
else:
    print("It's not an arithmetic operation")

Alternatively you can do this without any of those variables. Just put the calculations in the first set of if statements:

f_n = input('Type in your first number: ')
s_n = input('Type in your second number: ')
math = input('What are we doing? ')

if math == '*':
    print(f'Your answer is: {int(f_n) * int(s_n)}')
elif math == '+':
    print(f'Your answer is: {int(f_n) + int(s_n)}')
elif math == '-':
    print(f'Your answer is: {int(f_n) - int(s_n)}')
elif math == '/':
    rint(f'Your answer is: {int(f_n) / int(s_n)}')
else:
    print("It's not an arithmetic operation")