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编辑端：

import pygame
  pygame.init() keep_going = True
X = 0 Y = 0 while keep_going:     screen = pygame.display.set_mode([800, 800])     for event in pygame.event.get():         if(event.type == pygame.QUIT):             keep_going = False     screen.blit(pic,(x,y))_________________line 17     pygame.display.update()     x = (x + 1)     y = (y + 1)   t = (255, 255, 255) screen.fill(t) pygame.quit()   输出显示 nameEorror:name "pic" is not defined???   说eorror在17行___