save project

snake.py

@@ -54,7 +54,8 @@ while True:
         apple_x=30*random.randint(1,22)-30
         apple_y=30*random.randint(1,16)-30
     position.append((x, y))
-    position.pop(0)
+    else:
+        position.pop(0)
     # 将背景图画上去
     screen.blit(background, (0, 0))
     # 将贪吃蛇的头画上去