save project

snake.py

@@ -54,6 +54,8 @@ while True:
         y += 30
     position.append((x, y))
     position.pop(0)
+    if x<0 or x>630 or y<0 or y>530:
+        exit() 
     # 将背景图画上去
     screen.blit(background, (0, 0))
     # 将贪吃蛇的头画上去