save project

snake.py

@@ -62,11 +62,13 @@ while True:
         ya = n2 * 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
     screen.blit(snake_head, position[-1])
-    # 将贪吃蛇的身体画上去
+    # 将贪吃蛇的身体画上 
     for i in range(len(position)-1):
         screen.blit(body, position[i])