第三章 文件操作

文件操作分为 读 写 修改 

示例：

f =open(file='db.txt',mode='r',encoding='utf-8')   r 只读 r+ 读写 w+ 写读 w 写  rb  以二进制方式读取  a 把内容追加到文件尾部

data=f.read()

f.close()

循环文件

f = open(file='db.txt','r',encoding="utf-8")

for line in f :

    print (line)

f.close()

写文件

f = open(file='db.txt','w',encoding="utf-8")

f.write('aslkfladfasdf')

f.close()

占硬盘方式的文件修改代码示例

模拟登陆

import os

f = oopen(f_name,'r',encoding='utf-8')

f_new=open(f_new_name,'w',encoding='utf-8')

for line in f:

    if old_str in line:

        new_line = line.replace(old_str,new_str)

    else:

        new_line = line

    f_new.write(new_line)

f.close()

f_new.close()

os.rename(f_new_name,f_name)

while True:

name=input('请输入用户名>>:  ')

with open ('lock.txt','r',encoding='utf-8') as read_f:

 f=read_f.read()

if name in f:

    print('次用户已锁定‘）

break 

psw=input('请输入密码>>: ')

with open ('user.txt','r',encoding='utf-8') as read_f:

for line in read_f:

    l=line.strip().split(',')

   if name==l[0] and psw==l[1]:

    print(‘登陆成功’’)

    break

    else:

   

       print('请重新输入')

     count+=1

  if count=3 :

 with open ('lock.txt','w',encoding='utf-8') as write_f:

    write_f.write(name)

    print('用户已锁定')

    break

全局替换

import sys
import os 
count=0
if len(sys.argv) != 3:
    print('usage: cp source_file target_file')
    sys.exit()

old_str,new_str=sys.argv[1],sys.argv[2] 
with open(f_new_name,'rb') as f,open(f_new_name,'wb') as f_new:

for line in f:
if old_str in line:
    new_line=line.replace(old_str,new_str)
    count+=1
else:
    new)line=line
f_new.write(new_line)
os.rename(f_new_name,f_name)
print('count')