三级菜单-递归和堆栈的方法写

menu = {
    '北京': {
        '朝阳': {
            '国贸': {},
            'CICC': {},
            'HP': {},
            '渣打银行': {},
            'CCTV': {},
        },
        '望京': {
            '陌陌': {},
            '奔驰': {},
            '360': {},
        },
        '三里屯': {
            '优衣库': {},
            'apple': {},
        },
        '昌平': {
            '沙河': {
                '老男孩': {},
                '阿泰包子': {},
            },
            '天通苑': {
                '链家': {},
                '我爱我家': {},
            },
            '回龙观': {},
        },
        '海淀': {
            '五道口': {
                '谷歌': {},
                '网易': {},
                'sohu': {},
                '快手': {},
            },
            '中关村': {
                'youku': {},
                'Iqiyi': {},
                '汽车之家': {},
                '新东方': {},
                'QQ': {},
            },

        },
    },
    '上海': {
        '浦东': {
            '陆家嘴': {
                'CICC': {},
                '高盛': {},
                '摩根': {},
            },
        },
        '闵行': {},
        '静安': {},
    },
    '山东': {
        '济南': {},
        '德州': {
            '乐陵': {
                '丁务镇': {},
                '城区': {},
            },
            '平原': {},
        },
        '青岛': {},
    },
}
#
def threeLM(dic):
    while True:
        for k in dic:
            print(k)
        key =input('input>>>').strip()
        if key =='b' or key=='q':
            return key
        elif key in dic.keys() and dic[key]:
            ret = threeLM(dic[key])
            if ret =='q':
                return 'q'

threeLM(menu)

l =[menu]
while l:
    for key in l[-1]:
        print(key)
    k =input('input>>').strip()
    if k in l[-1].keys() and l[-1][k]:
        l.append(l[-1][k])
    elif k =='b':l.pop()
    elif k =='q':break
    else:continue