我用Pygame Zero和MU IDE创建了一个小游戏。游戏结束后，应该询问用户是否想再玩一次。如果他选择是，游戏应该从头开始。我知道我可以用While循环来做到这一点，但我不知道怎么做。
我试图插入一个while循环。在while循环中，游戏函数被调用，但它不起作用。我尝试了这个：

play_again = raw_input("If you'd like to play again, please type 'yes'")
while playagain == "yes"
      draw()
      place_banana()
      on_mouse_down(pos)
      update_time_left()

....
我知道这样做是不对的，但我不知道如何做才对

from random import randint 
import time
import pygame

HEIGHT = 800
WIDTH = 800
score = 0 
time_left = 10

banana = Actor("banana")
monkey = Actor("monkey")

def draw():
    screen.clear()
    screen.fill("white")
    banana.draw()
    monkey.draw()
    screen.draw.text("Number of bananas collected: " + str(score),      color = "black", topleft=(10,10))
    screen.draw.text("Time: " + str(time_left), color = "black", topleft=(10,50))

def place_banana():
    banana.x = randint(125, 790)
    banana.y = randint(186, 790)
    monkey.x = 50
    monkey.y = 740

def on_mouse_down(pos):
    global score
    if banana.collidepoint(pos): 
        score = score + 1 
        place_banana()

 def update_time_left():
    global time_left
    if time_left:  
         time_left = time_left - 1
    else:  
        screen.fill("pink")  # code is not executed
        game_over() 

place_banana() 
clock.schedule_interval(update_time_left, 1.0)

def game_over():
    screen.fill("pink") # code is not executed
    global time_left
    message = ("Ende. Number of bananas collected")   # code is not   executed
    time_left = 0
    time.sleep(5.5)
    quit()