When the user inputs anything but a number for the first input, the program should quit. But instead it just keeps going.

I tried to put many if ... break statements in the main function after the "a" to break it, but nothing helped.

def is_number(str):
    try:
        float(str)
        return True
    except ValueError:
        return False
       

def is_valid_operator(operator):
    operators = (' ', '-', '*', '/')
    return operator in operators



def ask_for_a_number(force_valid_input):
    while force_valid_input is True:
        a = input('Please provide a number: ')
        if is_number(a):
            return float(a)
        else:
            if not force_valid_input:
                return None
            print("This doesn't look like a number, try again!")

def ask_for_an_operator(force_valid_input):
    while force_valid_input is True:
        operator = input('Please provide an operator: ')
        if is_valid_operator(operator):
            return operator
        else:
            if not force_valid_input:
                return None
            print('Unknown Operator')



def calc(operator, a, b):
    if not is_number(a) or not is_valid_operator(operator) or not is_number(b):
        return None
    result = 0
    if operator == ' ':
        result = a   b
    elif operator == '-':
        result = a - b
    elif operator == '*':
        result = a * b
    elif operator == '/':
        if b != 0:
            result = a / b
        else:
            print('Error: Divide by zero is not allowed')
            return None

    return result

def main():
    while True:
        a = ask_for_a_number(force_valid_input = True)
        operator = ask_for_an_operator(force_valid_input = True)
        b = ask_for_a_number(force_valid_input = True)
        result = calc(operator, a, b)
        if result is not None:
            print(f'The result is {result}')
    
    


if __name__ == '__main__':
    main()

CodePudding user response：

Your main problem is that you are using a while loop with True but never order it to stop. You'd need a break somewhere in there. On another note, you don't need to check if a boolean is True, you can just do if bool or while bool as it returns True or False anyway.

CodePudding user response：

You can just add a condition like below in main function

 a = ask_for_a_number(force_valid_input = True)
 if a == 'break': 
  break

And in the function ask_for_a_number return the 'break' string like below

 print("This doesn't look like a number, try again!");
 return 'break'

CodePudding user response：

You check whether a is a number or not, but then don't do anything if it isn't one. So check the value of a

a = ask_for_a_number(force_valid_input = True)
if not a:
    return