python 三级菜单 的另1种实现方法

menu = {
 "华南":{
  "广东":["广州市","佛山市","深圳市","东莞市"],

  "广西":["南宁市","柳州市","桂林市","北海市"],


  "海南":["海口市","三亚市","三沙市","儋州市"]

 },
 "华东":{
  "上海":["黄浦区","卢湾区","徐汇区","长宁区","普陀区"],

  "安徽":["合肥市","芜湖市","淮南市","马鞍山市"],

  "江苏":["南京市","无锡市","徐州市","常州市","苏州市"]

 },
 "华北":{
  "北京":["东城区","西城区","朝阳区","丰台区","石景山区","海淀区"],

  "山西":["太原市","大同市","阳泉市","长治市"],

  "河北":["石家庄市","唐山市","秦皇岛市","邢台市"]

 },
 "华中":{
  "湖北":["武汉市","黄石市","十堰市","十堰市"],

  "河南":["郑州市","开封市","洛阳市","平顶山市"],

  "湖南":["长沙市","株洲市","衡阳市","邵阳市"]

 },
 "西南":{
  "重庆":["万州区","涪陵区","渝中区","大渡口区"],
  "四川":["成都市","自贡市","攀枝花市","德阳市"],
  "贵州":["贵阳市","六盘水市","遵义市","安顺市"],


 },
 "特别行政区":{
  "香港":["屯门","弯仔","北角","西贡"],
  "澳门":["花地玛堂区","圣安多尼堂区","大堂区","望德堂区"],

 },


}

last = [menu]
now = menu
while True:
    for key in now:
        print(key)
    choice = input('>>>:').strip()
    if choice == 'q':
        break
    if choice == 'b':
        now = last[-1]
        last.pop()
    if choice in now:
        last.append(now)
        now = now[choice]