python - while 循环在抛出垃圾值时不会重复自身

Question

我正在尝试使用“not”关键字运行 while 循环，但是当我这样做时，循环也接受垃圾值(例如 bjskdjb)，这不是 while/for 循环设置的条件.

当我运行 for 循环时，它抛出语法错误。

我在这里犯了什么错误(使用 for 循环和 while 循环)？

我尝试过使用 for 循环和 while 循环来实现。

def askplayerchoice():
    playerchoice = ''
    while playerchoice not in ('X' , 'O'):
        playerchoice = input('Enter X or O: ')
        if playerchoice == 'X':
            return ['X' , 'O']
        else:
            return ['O', 'X']
askplayerchoice()

'''
# Using For loop I am getting a syntax error. 

def askplayerchoice():
    playerchoice = ''
    for playerchoice not in ('X' , 'O'):
        playerchoice = input('Enter X or O: ')
        if playerchoice == 'X':
            return ['X' , 'O']
        else:
            return ['O', 'X']
askplayerchoice()

'''

我希望代码不断要求用户输入“X”或“O”，直到用户输入正确的值。

Answer 1

您可以添加一个 try catch block ，并在输入的字符串与您想要的值不匹配时抛出异常。我已经更新了你的代码。以下是片段:

def askplayerchoice():
    playerchoice = ''
    while playerchoice.lower() not in ('X' , 'O'):
        try:
            playerchoice = str(input('Enter X or O: '))
            if playerchoice.lower() not in ['x','o']:
                raise ValueError('A very specific bad thing happened.')
            if playerchoice.lower() == 'x':
                return ['X' , 'O']
            else:
                return ['O', 'X']
        except ValueError:
            playerchoice = ''


askplayerchoice()