ValueError: invalid literal for int() with base 10: ' ' but in debugger it has a value

Question

program is at the bottom

In my program im trying to make a working calculator, i have the loops down, entering valid operators, different operators, and now im trying to allow previous answers to be used.

lets say you use +, addition

num1 = 5

num2 = 5

then print (num1+num2)...etc

now the answer is 10 so i assign prevAnswer to answer and now they are both 10

one of my if loops is the following:

    if num2 == 0:
    prevAnswer = num1
    num1 = num2
    num2 = prevAnswer

I initialized num2 as an int and the value of 0, so if the user doesn't enter anything it should be 0 right? then I make the num1 = the previous answer and num2 = num1, swapping variables so if i were to have the previous value of 15 then I wouldn't have 5 - 15 = -10 as that wouldn't make sense in a calculator.

I've ran my program in debugger and at the time of (value error invalid literal for int() with base 10: '') this is where it says the error is:

num2 = int(input("Enter number 2: "))

in debugger at this error these are my variables, answer is int 8, num1 is int 2, num2 is int 3, operator is string +, prevAnswer is int 8, ive tried over loading my code with int() so this would work and nothing i seem to try changes anything it just gives me value errors or name errors

please try to ignore the mess of ints and everything i know there is definitely things here that i dont need and i will learn to use define functions to make everything better looking for others and easier for myself. i just have no idea where ive gone wrong ive searched up all the errors i got and i cant use any of the functions or solutions they use it just gives me other errors. finally, sorry about the indentation, this isnt what my program looks like and i assume it wont run unless you auto indent.

def isExitCommand(userInput):
return (userInput == 'exit' or userInput == 'stop' or userInput == 'Exit' or userInput == 'EXIT' or 
userInput ==
        'Stop' or userInput == 'STOP')


def calc_exponent(num, pow):
result = 1
for i in range(pow):
    result = result * num
return result


num1 = int(0)
num2 = int(0)
while True:
operator = str(input("Would you like to add(+), subtract(-), multiply(*), divide(/) or use 
exponents(**)? "))

if isExitCommand(operator):
    break

num1 = int(input("Enter number 1: "))
if isExitCommand(num1):
    break
else:
    num1 = int(num1)

num2 = int(input("Enter number 2: "))
if num2 == 0:
    prevAnswer = num1
    num1 = num2
    num2 = prevAnswer

if isExitCommand(num2):
    break

else:
    num2 = int(num2)

    if operator == 'add' or operator == '+':
        answer = int(num1) + int(num2)
        print(num1, '+', num2, '=', answer)

    elif operator == 'subtract' or operator == '-':
        answer = int(num1) - int(num2)
        print(num1, '-', num2, '=', answer)

    elif operator == 'multiply' or operator == '*':
        answer = int(num1) * int(num2)
        print(num1, '*', num2, '=', answer)

    elif operator == 'divide' or operator == '/':
        answer = int(num1) / int(num2)
        print(num1, '/', num2, '=', answer)

    elif operator == 'exponents' or operator == '**':
        num1 = int(num1)
        num2 = int(num2)
        answer = calc_exponent(num1, num2)
        print(num1, '**', num2, '=', answer)
    else:
        print('Please type a valid operator...')

prevAnswer = answer

print('Program has exited due to user input.')

Answer 1

If the user doesn't enter anything, the string value is "" (empty) which has an error when converting to int.

A quick solution is to replace the empty input with 0:

num1 = int(input("Enter number 1: ") or 0)  # use 0 if empty input

Output

Would you like to add(+), subtract(-), multiply(*), divide(/) or use exponents(**)? +
Enter number 1:
Enter number 2: 34
0 + 34 = 34