screen,COLORS['darkgray'],(xy[0]-WALL_WIDTH/2,xy[1]-WALL_WIDTH/2,WALL_WIDTH,WALL_HEIGHT),0)
# 绘制蛇,包括头和身体...'
elif event.key == K_RIGHT:
if head in ['up','down']:
head = 'right'
elif event.key == K_UP...:
if head in ['left','right']:
head = 'up'
elif event.key == K_DOWN:
if head in ['left...if head in ['up','down']:
head = 'right'
elif event.key == K_UP...if head in ['left','right']:
head = 'up'
elif event.key == K_DOWN