python_文件的处理

import osdef deluser(username):    '''    删除用户名    :param username:     :return:     '''    with open('db.text','r') as f1 :        lines = []        is_user=user_exist(username)        print(is_user)        if is_user:            for line in f1:                line1 = line.strip()                line_list = line1.split('$')                if username == line_list[0]:                    continue                else:                      lines.append(line)    open('db.text', 'w').writelines(lines)def  login(username,pwd):    '''    用户名密码登陆判断    :param username: 用户名    :param pwd: 密码    :return: True 登陆成功 False 登录失败    '''    with open('db.text') as user_pwd:        for line in  user_pwd:            line=line.strip()            longinlist=line.split("$")            if username==longinlist[0] and pwd==longinlist[1]:                return True    return Falsedef register(username,pwdword):    '''    注册用户    :param username:     :param pwdword:     :return:     '''    with open('db.text','a') as f:        f.write('\n'+username+'$'+pwdword)def user_exist(username):    '''    判断用户名是否存在    :param username:     :return:     '''    with open('db.text') as  f:        for line in f:            line = line.strip()            line_list = line.split('$')            if line_list[0] == username:                return True    return  Falseprint('欢迎登陆')inp=int(input("1:登陆 2:注册"))if inp==1:    username=input('请输入用户名')    pwd=input('请输入密码')    is_login=login(username,pwd)    if is_login:        print("登陆成功")    else:        print("登陆失败")elif inp == 2:    username = input('请输入用户名')    if user_exist(username):        print("已经注册过了")    else:        pwd = input('请输入密码')        register(username,pwd)        print('注册成功')elif inp == 3:    username = input('请输入用户名')    deluser(username)