save project

snake.py

@@ -62,7 +62,8 @@ while True:
     else:
         position.pop(0)
     position.append((x, y))
-    
+    if x<0 or y<0 or x>630 or y<450:
+        exit()
     # 将背景图画上去
     screen.blit(background, (0, 0))
     # 将贪吃蛇的头画上去