python三级菜单

menu = {
 '北京':{
 '海淀':{
 '五道口':{
 'soho':{},
 '网易':{},
 'google':{}
 },
 '中关村':{
 '爱奇艺':{},
 '汽车之家':{},
 'youku':{},
 },
 '上地':{
 '百度':{},
 },
 },
 '昌平':{
 '沙河':{
 '老男孩':{},
 '北航':{},
 },
 '天通苑':{},
 '回龙观':{},
 },
 '朝阳':{},
 '东城':{},
 },
 '上海':{
 '闵行':{
 "人民广场":{
 '炸鸡店':{}
 }
 },
 '闸北':{
 '火车战':{
 '携程':{}
 }
 },
 '浦东':{},
 },
 '山东':{},
}

while True:
 for key in menu:
 print(key)
 choice = input(">>>:")
 if len(choice) == 0: continue
 if choice not in menu:continue
 while True:
 for key2 in menu[choice]:
 print(key2)
 choice2 = input(">>>:")
 if len(choice2) == 0: continue
 if choice2 == "b": break
 if choice2 not in menu[choice]: continue
 while True:
 for key3 in menu[choice][choice2]:
 print(key3)
 choice3 = input(">>>:")
 if len(choice3) == 0: continue
 if choice3 == "b": break
 if choice3 not in menu[choice][choice2]: continue
 while True:
 for key4 in menu[choice][choice2][choice3]:
 print(key4)
 choice4 = input(">>>:")
 if len(choice4) == 0: continue
 if choice4 == "b": break
 if choice4 not in menu[choice][choice2][choice3]: continue

current_level = menu
last_level = []
while True:
 for key in current_level:
 print(key)
 choice = input(">>>:")
 if len(choice) == 0:continue
 if choice == "b":
 if not last_level : break
 current_level = last_level[-1]
 last_level.pop()
 if choice not in current_level:continue
 last_level.append(current_level)
 current_level = current_level[choice]