[FIXED] Why python code accepts '.' and '-' as numbers?

Issue

Use case: ATM machines allow 4 or 6 digit PIN codes and PIN codes cannot contain anything but exactly 4 digits or exactly 6 digits.

If the function is passed a valid PIN string, return true, else return false.

My code is working for all the randomly generated pins except for:

'12.0' '1234.0' '111-' '44444-'

def validate_pin(pin):
    numbers = '0123456789'
    if len(pin) != 4 and len(pin) != 6:
        return False
    else:
        for i in range(len(pin)):
            if pin[i] in numbers:
                return True
            else:
                break
        return False

Any idea why this would be? These characters do not live within my created variable.

Solution

As kaya3 suggested, the best way to solve issues like this is to step through with a debugger. You can do this in VS code by hitting "Run and Debug" on the debug tab shown below:

Basically your code is checking if the first character is in numbers or not. If it is a number, the for loop breaks, if it isn't, the for loop breaks. Here's a small fix:

def validate_pin(pin):
numbers = '0123456789'
if len(pin) != 4 and len(pin) != 6:
    return False
else:
    for i in range(len(pin)):
        if pin[i] not in numbers:
            return False
        # if pin[i] in numbers:
        #     return True
        # else:
        #     break
    return True

Answered By - Barnaby