python_文件的处理

import os

def 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("$")
            if username==longinlist[0] and pwd==longinlist[1]:
                return True
    return False
def register(username,pwdword):
    '''
    注册用户
    :param username: 
    :param pwdword: 
    :return: 
    '''
    with open('db.text','a') as f:
        f.write('\n'+username+'$'+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  False



print('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)