Why is my function always outputting "invalid" as a result?

I am learning python. In this context, I do an exercise in which I need to perform a series of test on a string. If these checks are met, python should output "Valid", if not "Invalid".

Here is my code, with the comments describing the goal of each functions:

import string

def main():
    plate = input("Plate: ")
    if is_valid(plate):
        print("Valid")
    else:
        print("Invalid")

# Function "main" calls the "is_valid" function

def is_valid(s):
    if lenght_valid(s) == True and starts_alpha(s) == True and check_ponctuation(s) == False:
        return True
    else:
        return False

# Function "is_valid" calls all the other function checking single cirterias

def lenght_valid(s):
    if len(s) > 6 or len(s) < 2:
       return False
    else:
       return True

# Function "lengt_valid" check the propoer lenght (2 characters min., 6 max.)


def starts_alpha(s):
    s = s[0:2]
    if s.isalpha():
       return True
    else:
       return False

# Function "starts_alpha" check that the first two characters are letters

def check_ponctuation(s):
    return (character in string.punctuation for character in s)

# Function "check_punctuation" checks if punctuation is present. If "True" then this will be rejected in the above function

main()

I do not understand why it always outputs "Invalid". I tested "KA" and "KOKO" and these should be valid, however, these are not valid.

>Solution :

Your function, check_ponctuation is returning a generator, not a boolean result.

def check_ponctuation(s):
    return (character in string.punctuation for character in s)

This function is not doing what you think it is doing.

Presumably, you’ve missed an any() call.

This code is what it should be:

def check_ponctuation(s):
    return any(character in string.punctuation for character in s)

The reason that any is needed, is that if you call

return (character in string.punctuation for character in s)

by itself, you’re returning a generator object which could result in undefined behavior.

Instead, by using any(), you can check to see if your string contains any punctuation and return a true or a false based on that.

Here’s some information about any() in python and how it works:

"The any() function returns True if any item in an iterable are true, otherwise it returns False.

If the iterable object is empty, the any() function will return False."

https://www.w3schools.com/python/ref_func_any.asp