三级地名菜单

menu={
    "北京":{
        "朝阳":{...},
        "昌平":{
            "沙河":{
                "老男孩":{},
                "阿泰包子":{},
            },
            "天通苑":{...},
            "回龙观":{},
            },
            "海淀":{...},
    },
    "上海":{...},
    "山东":{...},
}

current_layer = menu
parent_layers =[]
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)
        current_layer =current_layer[choice]
    elif choice == "b":
        if parent_layers:
            current_layer = parent_layers.pop()
    else:
        print("无此项")
        print("请重新输入")