一.利用b模式，编写一个cp工具，要求如下：

1. 既可以拷贝文本又可以拷贝视频，图片等文件

2. 用户一旦参数错误，打印命令的正确使用方法，如usage: cp source_file target_file

提示：可以用import sys，然后用sys.argv获取脚本后面跟的参数

#!/usr/bin/env python3

# -*- coding:utf-8 -*-

# cp工具

import sys

if len(sys.argv) != 3:

print("usage: cp source_file target_file")

sys.exit()

else:

source_file, target_file = sys.argv[1], sys.argv[2]

with open(source_file,"rb") as read_f,open(target_file,"wb") as write_f:

for line in read_f:

write_f.write(line)

二.Python实现 tail -f 功能

#!/usr/bin/env python3

# -*- coding:utf-8 -*-

#tail -f工具

import sys,time

if len(sys.argv) != 2:

print("usage: tail file_name")

sys.exit()

else:

file_name = sys.argv[1]

with open(file_name,'rb') as f:

f.seek(0,2) # 每次都从文件末尾开始读

while True:

line = f.readline()

if line:

print(line.decode('utf-8'),end='') # 读取的每一行都去掉行尾的换行符

time.sleep(1)

有待优化，每次打开应该显示最后10行。

三.文件的修改

文件的数据是存放于硬盘上的，因而只存在覆盖、不存在修改这么一说，我们平时看到的修改文件，都是模拟出来的效果，具体的说有两种实现方式：

方式一：将硬盘存放的该文件的内容全部加载到内存，在内存中是可以修改的，修改完毕后，再由内存覆盖到硬盘(word，vim，nodpad++等编辑器)

import os

with open('a.txt') as read_f,open('.a.txt.swap','w') as write_f:

data=read_f.read() #全部读入内存,如果文件很大,会很卡

data=data.replace('alex','SB') #在内存中完成修改

write_f.write(data) #一次性写入新文件

os.remove('a.txt')

os.rename('.a.txt.swap','a.txt')

方式二：将硬盘存放的该文件的内容一行一行地读入内存，修改完毕就写入新文件，最后用新文件覆盖源文件

import os

with open('a.txt') as read_f,open('.a.txt.swap','w') as write_f:

for line in read_f:

line=line.replace('alex','SB')

write_f.write(line)

os.remove('a.txt')

os.rename('.a.txt.swap','a.txt')

三.全局替换程序：

写一个脚本，允许用户按以下方式执行时，即可以对指定文件内容进行全局替换

替换完毕后打印替换了多少处内容

#!/usr/bin/env python3

# -*- coding:utf-8 -*-

import sys

import os

if len(sys.argv) != 4:

print("usage: python3 replace old_str new_str filename")

sys.exit()

else:

old_str = sys.argv[1]

new_str = sys.argv[2]

filename = sys.argv[3]

filename_swap = sys.argv[3] + ".swap"

with open(filename,"r",encoding="utf-8") as read_f,open(filename_swap,"w",encoding="utf-8") as write_f:

count = 0

for line in read_f:

line = line.replace(old_str,new_str)

write_f.write(line)

num = line.count(new_str)

count += 1

totle = count * num

print("一共替换了%s处内容" % totle)

os.remove(filename)

os.rename(filename_swap,filename)

四.模拟登陆：

用户输入帐号密码进行登陆

用户信息保存在文件内

用户密码输入错误三次后锁定用户，下次再登录，检测到是这个用户也登录不了

user_list.txt

wss:123:1

alex:456:1

jay:789:1

#!/usr/bin/env python3

# -*- encoding: utf8 -*-

import getpass

import os

user_dict = {}

with open("user_list.txt", "r", encoding="utf-8") as user_list_flie:

for line in user_list_flie.readlines():

user_list = line.strip().split(":")

# print(user_list)

_user = user_list[0].strip()

_pwd = user_list[1].strip()

_lockaccount = int(user_list[2].strip())

user_dict[_user] = {"user": _user, "pwd": _pwd, "lockaccount": _lockaccount}

# print(user_dict[_username])

# print(user_dict)

exit_flag = False

count = 0

while count < 3 and not exit_flag:

user = input('\n请输入用户名:')

if user not in user_dict:

count += 1

print("\n用户名错误")

elif user_dict[user]["lockaccount"] > 0:

print("\n用户已被锁定,请联系管理员解锁后重新尝试")

break

else:

while count < 3 and not exit_flag:

pwd = getpass.getpass('\n请输入密码:')

# pwd = input('\n请输入密码:')

if pwd == user_dict[user]["pwd"]:

print('\n欢迎登陆')

print('..........')

exit_flag = True

else:

count += 1

print('\n密码错误')

continue

if count >= 3: # 尝试次数大于等于3时锁定用户

if user == "":

print("\n您输入的错误次数过多,且用户为空")

elif user not in user_dict:

print("\n您输入的错误次数过多,且用户 %s 不存在" % user)

else:

user_dict[user]["lockaccount"] += 1

# print(user_dict[user]["lockaccount"])

with open("user_list.txt", "r", encoding="utf-8") as user_list_file, open("use_list.txt.swap", "w",encoding="utf-8") as new_user_list_file:

for new_line in user_dict:

new_user_list = [str(user_dict[new_line]["user"]), str(user_dict[new_line]["pwd"]),

str(user_dict[new_line]["lockaccount"])]

# print(new_user_list)

user_str = ":".join(new_user_list)

print(user_str)

new_user_list_file.write(user_str + "\n")

os.remove("user_list.txt")

os.rename("use_list.txt.swap", "user_list.txt")

print("\n您输入的错误次数过多,%s 已经被锁定" % user)