Python note 13-file read and write

1. Open File

F=open (' a.txt ', ' A + ', encoding= ' utf-8 ') #f代表的是文件对象, called a handle

F.seek (0) Put the file pointer to the front

There are 3 types of File open modes:

1:w write mode, it is unreadable, when using W it will empty the original content and then write

w+ write mode, when using W, it will empty the original content and then write

2:R read mode, can only read and cannot write, and the file must exist

r+ read-write mode, the original file still exists, but if the file does not exist will be an error

3:A Append mode, write only, add content at the end of the file

A + can read and write, the default file pointer in the last

4:rb+, wb+,ab+, this is binary mode open or read, some music files, pictures and so on

F=open (' a.txt ') #如果在打开的文件的时候, do not specify mode, that is, read mode

The file object is also iterative, read-only 1 lines of content, this high efficiency

For line in F: #f代表文件对象

Print (line) #打印每行内容

#直接循环文件对象的话, looping through the contents of each line of the file

2. Read the contents of the file

Print (F.read ()) #读文件全部内容, returns a string

Print (F.readlines ()) #读文件全部内容, returns a list

Print (F.readline ()) #读文件一行内容, can read only one line at a time

3. Writing content

F.write (' hhh ') #写文件, writing a string

F.writelines ([' 123 ', ' 345 ', ' 567 ']) #可以把列表写入文件

4. File modification

 # res = F.read () #打开文件  
 # f.seek (0) #指针  
 # f.truncate () #清空文件内容  
 # new_res = Res.replace (' Nihao ', ' Nibuhao ') #把nibuhao replace Nihao  
 # f.write (new_res) Read new content  
  #以上方法, reading for large files is not available  
 
 

  important: each line reads and puts a new file:  
 import os  
 f=open (' a.txt ', ' A + ', encoding= ' utf-8 ') #打开文件  
 # fw = open (' A.txt.new ', ' W ', encoding= ' utf-8 ') #把替换好的文件放入到fw文件中  
 # for line in F:  
 # new_res = line.replace (' Learn ', ' don't Learn ')  
 # fw.write (new_res)  
 # F.close () # Close F file  
 # fw.close () #关闭fw文件  
 # Os.remove (' a.txt ') #删除文件  
 # os.rename (' a.txt.new ', ' a.txt ') #重命名把a. txt.new Rename to A.txt  
 
 5.flush usage, with usage  

#flush用法
Import time
FW = open (' Python.txt ', ' W ', encoding= ' utf-8 ')
Fw.write (' No class next week! ‘)
Fw.flush () #写完之后立马生效
Exit (' Goodbye ')
Time.sleep (#程序休息30秒)
Fw.close ()


#with的用法, when your file is no longer in use, it will automatically close the file to you
# with open (' Python.txt ', encoding= ' Utf-8 ') as fr:
#     Print (Fr.read ())

Python note 13-file read and write