save project

snake.py

@@ -63,6 +63,9 @@ while True:
         position.pop(0)
     if x<0 or x>630 or y<0 or y>450:
         exit()
+    for i in range(len(position)-1):
+        if (x,y)==position[i]:
+            exit()  
     position.append((x, y))
     # 将背景图画上去
     screen.blit(background, (0, 0))