控件在第二次迭代中跳过函数。为什么?

我的代码:

def player_input():
    global symbol1
    global symbol2
    """
    do something
    """
    marker=True      

def replay():
    game=True
    while(game==True):

        print('do you want to play?')
        option=input(' enter yes/no ')              
        if option=='no':
            game=False
            break
        while not(option=='YES'): 
            option=input('choose the right option')

        marker=player_input()

    print('see you around!...bye')


symbol1=''
symbol2=''
replay()

do you want to play?

 enter yes/no   yes

player1 :  x

player2 :  o

do you want to play?

 enter yes or no       yes

do you want to play?

 enter yes or no        

控件没有进入函数:player\u input for second iteration。