为什么会报错呀？该怎么修改？

#!--*--coding:utf8--*--
from 练习.file import r_file, file
from 练习.login import login
from 练习.loginuser import login_name


def call():
    if login_name in r_file():
        login()
    else:
        print('该用户未注册，是否去注册？'
               'y,去注册')
        choose = input('请输入你的选择>>>:')
        if choose == 'y':
             ret = file()
        else:
            login()
    return login_name


if __name__ == '__main__':
    call()

请输入用户名>>>>:123

Traceback (most recent call last):
  File "D:/Program/小游戏/练习/main.py", line 22, in <module>
    call()
  File "D:/Program/小游戏/练习/main.py", line 8, in call
    if login_name in r_file():
  File "D:\Program\小游戏\练习\file.py", line 16, in r_file
    for user in f.readlines():
io.UnsupportedOperation: not readable

进程已结束，退出代码 1

报错的文件是file.py  应该是读取的文件的问题