python-三级菜单

'''程序: 三级菜单要求:打印省、市、县三级菜单可返回上一级可随时退出程序'''info = {    '北京':{        '昌平':{            '沙河':["oldboy","test"],            '天通苑':["我爱我家","链家地产"]        },        '朝阳':{            '望京':["奔驰","陌陌"],            '国贸':["CICC","HP"]        },        '海淀':{}    },    '上海':{        '浦东':[]    },    '广州':{},    '深圳':{}}exit_flag = Falsewhile not exit_flag:    for i in info:        print(i)    user_choice = input("你的选择是1>>>")    if user_choice in info:        while not exit_flag:            for i2 in info[user_choice]:                print("\t",i2)            user_choice2 = input("你的选择是2>>>")            if user_choice2 in info[user_choice]:                while not exit_flag:                    for i3 in info[user_choice][user_choice2]:                        print("\t\t",i3)                    user_choice3 = input("你的选择是3>>>")                    if user_choice3 in info[user_choice][user_choice2]:                        while not exit_flag:                            for i4 in info[user_choice][user_choice2][user_choice3]:                                print("\t\t\t",i4)                            user_choice4 = input("最后一层，请输入“b”返回>>>")                            if user_choice4 == "b":                                break                            elif user_choice4 == "q":                                exit_flag = True                    elif user_choice3 == "b":                        break                    elif user_choice3 == "q":                        exit_flag = True            elif user_choice2 == "b":                break            elif user_choice2 == "q":                exit_flag = True    elif user_choice == "b":        break    elif user_choice == "q":        exit_flag = True