save project

snake.py

@@ -67,6 +67,8 @@ while True:
         position.pop(0)
     # 将背景图画上去
     screen.blit(background, (0, 0))
+    if x<0 or x>630 or y<0 or y>450:
+        exit()
     # 将贪吃蛇的头画上去
     screen.blit(snake_head, position[-1])
     # 将贪吃蛇的身体画上去