data = {
    "华为技术":{
        "产品与解决方案":{
            "云核心网":{"云核心网研发管理部","云核心网平台开发部"},
            "无线网络产品线":{"无线研发管理部","无线平台开发部"  },
        },
        "2012实验室":{
            "质量与运营部":{"上研质量与运营部","成研质量与运营部"},
        },
        "物联网":{
            "车联网":{"车联网研发管理部","车联网开发管理部"},
        },
    },
}

exit_flag = False  # 默认不退出，

while not exit_flag:
    for i in data:
        print(i)
    user_choice = input("请选择您的一级SAP部门信息: ")
    if user_choice in data:
        while not exit_flag:
            for j in data[user_choice]:
                print("\t",j)
            user_choice_2 = input("继续选择您的二级SAP信息： ")
            if user_choice_2 in data[user_choice]:  #[user_choice_2]:
                while not exit_flag:
                    for k in data[user_choice][user_choice_2]:#[user_choice_3]:
                        print("\t\t",k)
                    user_choice_3 = input("继续选择您的三级SAP信息： ")
                    if user_choice_3 in data[user_choice][user_choice_2]:
                        for l in data[user_choice][user_choice_2][user_choice_3]:
                            print("\t\t",l)
                        user_choice_4 = input("达到最后一层了，返回请输入back:")
                        if user_choice_4 == "back":
                            break
                        elif user_choice_4 == "exit":
                            exit_flag = True
                            #pass 如果写pass，可以作为一个占位符，
                    if user_choice_3 == "back":
                        break
                    elif user_choice_3 == "exit":
                            exit_flag = True
            if user_choice_2 == "back":
                break
            elif user_choice_2 == "exit":
                exit_flag = True

    elif user_choice == "exit":
        exit_flag = True