简洁版三级菜单

此种方法省去的重复性的循环语句，用一个循环代替了所有

Menu = {
    "北京":{
            "昌平":["沙河","辛庄","南口"],
            "朝阳":["太阳宫","孙河","管庄"],
            "海淀":["上地","西三旗","西二旗"]
          },
    "河南":{
            "郑州":["二七区","中原区","金水区"],
            "洛阳":["西工区","老城区","洛龙区"]
            },
    "河北":{
            "石家庄":["新华区","长安区","正定县"],
            "邯郸":["丛台区","复兴区","大名县"]
        },
    "广东":{
            "广州":["南沙区","花都区","番禹区"],
            "深圳":["龙岗区","罗湖区","盐田区"],
            "东莞":["南城区","东城区","万江区"]
    },
}
cur_menu = Menu
parrent_menu = []
while True:
    for keys in cur_menu:
        print(keys)
    choice = input("请选择>>>").strip()
    if len(choice) == 0:
        continue
    if choice in cur_menu:
        parrent_menu.append(cur_menu)
        cur_menu = cur_menu[choice]
    elif choice == "b":
        if parrent_menu:
            cur_menu = parrent_menu.pop()
    else:
        print("输入错误，请重新输入")