python 实现三级菜单

info = {
    "广州":{"海珠":["江南西","昌岗东"],"天河":["天河南","东圃"],"荔湾":["中山五","上下九"]},
    "深圳":{"大亚湾":["很大","很小"],"前海":["大海","小海"]},
    "北京":{"二环":["很有钱","没钱"],"四环":["一般","穷"]}
}									#定义菜单，使用字典

back = True								#设置退出标识，为False则退出程序
while back:								#开始循环
    for i in info:
        print(i)							#打印菜单的键
    choice = input("选择城市，按q退出>>>")
    if choice in info:							#判断如果输入的结果在字典内，进入下一级菜单
        while back:
            for i2 in info[choice]:
                print(i2)						#循环二级菜单，打印键
            choice2 = input("选择地区，按b返回，按q退出>>>")
            if choice2 in info[choice]:					#判断如果输入的结果在字典内，进入下一级菜单
                while back:
                    for i3 in info[choice][choice2]:
                        print(i3)					#循环三级菜单，打印键
                    choice3 = input("最后一层，按b返回，按q退出")
                    if choice3 == "b":					
                        break						#判断如果输入b，退出当前循环返回上一级菜单
                    elif choice3 == "q":
                        back = False					#判断如果输入q，退出标识赋值为False，退出整个循环程序
            if choice2 == "b":
                break
            elif choice2 == "q":
                back = False
    elif choice == "q":
        back = False