day7 新三级菜单

 # 简单吧简单吧，用动态变量不停的改变进行遍历
 menu = {
     "北京":{
         "朝阳":{
                 "国贸":{
                     "CICC":{},
                     "HP":{},
                     "CCTV":{},
 },
                 "望京":{
                     "陌陌":{},
                     "奔驰":{},
                     ":{},
                 },
                 "三里屯":{
                     "优衣库":{},
                     "apple":{},
                 }
 },
         "昌平":{
             "沙河":{
                 "老男孩":{},
                 "阿泰包子":{},
             },
             "天通苑":{
                 "链家":{},
                 "我爱我家":{},
             },
             "回龙观":{},
         },
         "海淀":{
             "五道口":{
                 "谷歌":{},
                 "网易":{},
                 "Sohu":{},
                 "Sogo":{},
                 "快手":{},
                   },
             "中关村":{
                 "youku":{},
                 "Iqiyi":{},
                 "汽车之家":{},
                 "新东方":{},
                 "腾讯":{},

 },
 },
     },
     "上海":{
         "浦东":{
             "陆家嘴":{
                 "CICC":{},
                 "高盛":{},
                 "摩根":{},
             },
             "外滩":{},
         },
         "闵行":{},
         "静安":{},
         "":{},
     },
     "山东":{
         "济南":{},
         "德州":{
             "乐陵":{
                 "顶乌镇":{},
                 "城区":{},
             },
             "平原":{},
         },
         "青岛":{},
     },
 }

 current_layer = menu  #实现动态循环的初始变量
 # parent_layer = menu
 parent_layers = []    #保存父籍，最后一个元素永远都是父亲籍
 while True :
     for key in current_layer:
         print(key)
     choice = input(">>>:").strip()
     if    len(choice) == 0:continue
     if choice in current_layer:
         parent_layers.append( current_layer)   #在进下一层之前把当前层进行尾部追加，即下一层的父亲籍
         current_layer = current_layer[choice]  #将要被遍历的字典范围根据用户输入进行缩减范围
     elif choice == "b":
         if parent_layers:
             current_layer = parent_layers.pop()#进行最后一个的弹出并赋值返回父亲层
     else:
         print("无此项")