With作用：不用寫f.close,執行完with代碼塊，自動關閉相應文件
實例1：單個文件操作用with方法：

# -*-coding:utf-8 -*-
__author__ = ‘xiaojiaxin‘
__file_name__ = ‘with_method‘

f=open("log","r")
f.readline()
    f.read()
f.close()   #和下面的with等價

with open("log","r") as f:
    f.readline()
    f.read()
    #不再需要f.close().只要退出with代碼塊，自動close
 

實例2：多個文件操作用with方法

#創建操作多個文件，自動關閉
with open("log",‘r‘) as file1,open("paswd",‘r‘) as file2:
    file1.read()
    file2.read()

4.4文件操作：with