模拟三级菜单

exit_flag=False
data= {
    '北京':{
        "昌平":{
            '沙河':['oldboy','test'],
            '天通苑':['链家房产','我爱我家']
        },
    '朝阳':{
        "望京":['奔驰','陌陌'],
        '国贸':['CICC','HP'],
        '东直门':{'advent','飞信'},
    },
    '海绽':{},
    },
    '山东':{
        "德州":{},
        '青岛':{},
        '济南':{},
    },
    '广东': {
    "东莞": {},
    '常熟': {},
    '佛山': {},
},
}
while not exit_flag:
    for a in data:
        print(a)
    choice =input("请选择进入>>")
    if choice in data:
        while not exit_flag:
            for b in data[choice]:
                print('\t',b)
            choice2 = input("请选择进入2>>")
            if choice2 in data[choice]:
                while not exit_flag:
                    for c in data[choice][choice2]:
                        print('\t\t', c)
                    choice3 = input("请选择进入3>>")
                    if choice3 in data[choice][choice2]:
                        while True:
                            for d in data[choice][choice2][choice3]:
                                print('\t\t', d)
                            choice4=input(("当前访问最后一层，输入y可返回>>"))
                            if choice4=='y':
                                break
                            elif choice4=='q':
                                exit_flag==True
                    if choice3=='y':
                        break
                    elif choice3=='q':
                        exit_flag==True
            if choice2=='y':
                break
            elif choice2=='q':
                exit_flag==True