python 3级菜单程序

#!/usr/bin/env python
# -*- coding:utf-8 -*-
# Author:young
region = {
    "四川":{"巴中":{"平昌":["链家地产","平昌小学"],"南江":["南江幼儿园","南江广电"]},
           "德阳":{"中江":["中江挂面","中江表妹"],"什邡":["什邡板鸭","什邡米粉"]},
           "成都":{"锦江":["锦江幼儿园","春熙路商业街"],"成华":["烂尾楼","八里巷"]},
          },
    "黑龙江":{
          "哈尔滨":{"道外区":["道外高中","道外街道"],"松北区":["松花江","东北送花饼"],"平房区":["平房大学食堂","平房幼儿园"]}
         }}

exit_flag = False
while not exit_flag:
    for i in region:
        print(i)  # 打印一级地区，省级
    choice = input("请选择1:") #选择省级
    if choice in region:  # 判断输入省级是否存在
        while not exit_flag:
            for i2 in region[choice]:
                print("\t", i2)  # 打印选择省级的地市
            choice2 = input("请选择2:") #选择地市
            if choice2 in region[choice]:  # 判断输入地市是否存在
                while not exit_flag:
                    for i3 in region[choice][choice2]:
                        print("\t\t", i3)  # 打印地市的区县
                    choice3 = input("请选择3：") #选择区县
                    if choice3 in region[choice][choice2]:
                        for i4 in region[choice][choice2][choice3]:
                            print("\t\t", i4)
                        choice4 = input("已经是最后一层，按b返回>>:")
                        if choice4 == "b":
                            pass  #跳过，回到本次循环
                        elif choice4 == "q":
                            exit_flag = True
                        else:
                            print("您输入的参数有误！")
                    if choice3 == "b":
                        break     #跳过本次循环
                    elif choice3 == "q":
                        exit_flag = True
            if choice2 == "b":
                break
            elif choice2 == "q":
                exit_flag = True
    elif choice == "q":
        exit_flag = True
    else:
        print("您输入的省级不存在，请重新输入")