Question

I am still new to Python and have been reviewing the following code not written by me.

Could someone please explain how the first instance of the variable “clean” is able to be be called in the check_arguments function? It seems to me as though it is calling an as yet undefined variable. The code works but shouldn’t that call to “clean” produce an error?

To be clear the bit I am referring to is this.

def check_arguments(ages):
    clean, ages_list = parse_ages_argument(ages)

The full code is as follows…

def check_arguments(ages):
    clean, ages_list = parse_ages_argument(ages)
    if clean != True:
        print('invalid ages: %s') % ages
    return ages_list

def parse_ages_argument(ages):
    clean = True
    ages_list = []
    ages_string_list = ages.split(',')
    for age_string in ages_string_list:
        if age_string.isdigit() != True:
            clean = False
            break
    for age_string in ages_string_list:
        try:
            ages_list.append(int(age_string))
        except ValueError:
            clean = False
            break

    ages_list.sort(reverse=True)
    return clean, ages_list

ages_list = check_arguments('1,2,3')
print(ages_list)

Answer 1

how the first instance of the variable “clean” is able to be be called in the check_arguments function?

This is a nonsensical thing to ask in the first place, since variables aren’t called; functions are. Further, “instance” normally means “a value that is of some class type”, not “occurrence of the thing in question in the code listing”.

That said: the line of code in question does not use an undefined variable clean. It defines the variable clean (and ages_list at the same time). parse_ages_argument returns two values (as you can see by examining its return statement). The two returned values are assigned to the two variables, respectively.