作业9

编写文件修改功能，调用函数时，传入三个参数（修改的文件路径，要修改的内容，修改后的内容）

import os
def alter(file,old_str,new_str):
    with open(file, "r", encoding="utf-8") as f1, open("{}.swap".format(file), "w", encoding="utf-8") as f2:
        for line in f1:
            if old_str in line:
                line = line.replace(old_str, new_str)
            f2.write(line)
    os.remove(file)
    os.rename("{}.swap".format(file), file)

alter('file1','zc','牛逼')

既可完成文件的修改编写tail工具

import time
def tail(file):

    with open(file, 'rt', encoding='utf-8') as f:
        f.seek(0, 2)
        while True:
            res = f.readline()
            if not res:
                time.sleep(0.5)
            print(res)

编写登录功能
编写注册功能
编写用户认证功能

def login(username, password):
    """
    登录
    """
    with open('a.txt', 'r', encoding="utf-8") as f:
        for line in f:  # 一行一行的读取
            line = line.strip()  
            line_list = line.split(":")  
            if username == line_list[0] and password == line_list[1]:
                return True
    return False


def register(username, password):
    """
    注册
    """
    with open('a.txt', "a", encoding="utf-8") as f:

        f.write('{}:{}\n'.format(username,password))
    return True


def user_exist(username):
    '''
    验证用户注册是否存在
    '''

    with open('a.txt', "r", encoding="utf-8") as f:
        for line in f:
            line = line.strip()
            line_list = line.split(":")
            if username == line_list[0]:
                return True
    return False


def main():
    while True:
        msg = """
        0 退出
        1 登录
        2 注册
        """
        print(msg)
        cmd = input('请输入命令编号>>: ').strip()
        if not cmd.isdigit():
            print('必须输入命令编号的数字，傻叉')
            continue

        # 判断当前用户如果不在dic字典中，执行
        if cmd not in dic:
            print('输入的命令不存在')
            continue

        print(dic.get(cmd))
        if cmd=='1':
            user=input('请输入你的账号：').strip()
            pwd=input('请输入你的密码：').strip()
            is_login=login(user,pwd)
            if is_login:
                print('登录成功')
            else:print('登录失败')
        elif cmd=='2':
            user = input('请输入你的注册账号：').strip()
            pwd = input('请输入你的注册密码：').strip()
            is_exist=user_exist(user)
            if is_exist:
                print('用户已注册')
            else:
                result = register(user, pwd)
                if result:
                    print("注册成功")
                else:
                    print("注册失败")

main()