save project

snake.py

@@ -68,6 +68,8 @@ while True:
         apple_y=apple_ya*30
     else:    
         position.pop(0)
+    if x<0 or x>630 or y<0 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