python学习：跳出while循环的用法 exit_flag = False while not exit_flag:

三级菜单：
此处不足 没有考虑是否在data里面

# -*- coding:utf-8 -*-
# Author :deng
data = {
    '北京':{
        "昌平":{
            "沙河":["oldboy","test"],
            "天通苑":["链家地产","我爱我家"]
        },
        "朝阳":{
            "望京":["奔驰","陌陌"],
            "国贸":{"CICC","HP"},
            "东直门":{"Advent","飞信"},
        },
        "海淀":{},
    },
    '山东':{
        "德州":{},
        "青岛":{},
        "济南":{}
    }
}
exit_flag = False
while not exit_flag:
    for i in data:
        print(i)
    choice = input('请选择进入》》1:')
    if choice in data:
        while not exit_flag:
            for i2 in data[choice]:
                print('\t',i2)
            choice2 = input('请选择进入》》2:')
            if choice2 in data[choice]:
                while not exit_flag:
                    for i3 in data[choice][choice2]:
                        print('\t\t',i3)
                    choice3 = input('请选择进入》》3:')
                    if choice3 in data[choice][choice2]:
                        for i4 in data[choice][choice2][choice3]:
                                print('\t\t\t',i4)
                        choice4 =input('最后一层，输入b返回,退出选择q：')
                        if choice4 == 'b':
                            break
                        elif choice4 == 'q':
                            exit_flag = True
                    if choice3 == 'b':
                        break
                    elif choice3 == 'q':
                        exit_flag = True
            if choice2 == 'b':
                break
            elif choice2 == 'q':
                exit_flag = True