cs50p/problems/pset5/test_plates/plates.py

import re


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


def is_valid(s):
    if len(s) < 2 or len(s) > 6:
        return False
    return re.match(r"^[A-Z]{2,}([1-9]\d+)?(?![A-Z])$", s) is not None


def loopy_is_valid(s):
    length = 0
    has_digits = False
    for n, c in enumerate(s):
        if n > 6:
            return False
        if not c.isalnum():
            return False
        if n < 2 and not c.isalpha():
            return False
        if c.isdigit():
            if not has_digits and c == '0':
                return False
            has_digits = True
        elif has_digits:
            return False
        length += 1
    return length >= 2


if __name__ == "__main__":
    main()