plates.py

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


def is_valid(s):

    #“… maximum of 6 characters (letters or numbers) and a minimum of 2 characters.”
    if len(s) < 2 or len(s) > 6:
        return False

    #“All vanity plates must start with at least two letters.”
    if not s[0].isalpha() or not s[1].isalpha():
        return False

    #check if there is a digit
    pos = 0
    fdp = -1
    for c in s:
        if c.isdigit():
            fdp = pos
            break
        else:
            pos = pos + 1

    if fdp != -1:

        #The first number used cannot be a ‘0’.”
        if s[fdp] == '0':
            return False

        pos = 0
        for c in s:
            if pos>fdp and s[pos].isalpha():
                return False
            pos = pos + 1

    if not s.isalnum():
        return False

    return True

main()