新手请教，游戏入门程序 c

import sys
import pygame

def run_game():
    pygame.init()
    screen = pygame.display.set_mode((1200, 800))
    pygame.display.set_caption("Alien Invasion")

    while True:
        for event in pygame.event.get():
            if event.type == pygame.quit():
                sys.exit()

        screen.fill((200, 200, 200))
        pygame.display.flip()

这段代码运行结果是这样，请问什么问题啊？照着书本的范例写的。
Traceback (most recent call last):
  File "E:/My doc/Python/excersize/newgame/alien_invasion.py", line 36, in 
    run_game()
  File "E:/My doc/Python/excersize/newgame/alien_invasion.py", line 15, in run_game
    screen.fill((200, 200, 200))
pygame.error: display Surface quit

Process finished with exit code 1

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