输入中没有干预数字。 Python

Question

我试图弄清楚如何在while循环中包含以下要求“数字不能在[输入]中间使用；它们必须在末尾[例如AAA222有效但不是AAA22A]”。 代码通过了所有要求，但这个？ 关卡是“CS44P2”！ 也许我需要使用 for 循环来代替？

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
    if s[0].isdigit() == True or s[1].isdigit() == True:
        return False
    

#“All vanity plates must start with at least two letters.”
#“… vanity plates may contain a maximum of 6 characters     
#(letters or numbers) and a minimum of 2 characters.”
    
    c = 0
    while c < len(s):
        if s[c].isalpha() == False:
            if s[c] == '0':
                return False
            else:
                break
        c += 1

#"Numbers cannot be used in the middle #of a plate; they must come at the end."
    
    if s.isalnum() == False:
        return False

#“No periods, spaces, or punctuation #marks are allowed.”
    return True

main()