1. File Open
Here is the basic function for opening a
file
f = open(‘file’, ‘mode’)
there are multiple mode used in python
f is called file handler, that is the
object we used to control the file in further.
Common mode in python:
- a: append mode – append the content at the end of the file
- w: write mode – write the content into the file, it will erase the original conent of the file
- r: read mode – read the cotent from the file. The default mode.
- r+ : read and write mode
2. File Read
There are a few methods to read the content
from a file
f.readline() – just read one line from the
file, return a string
f.readlines() – read all lines and return a
list containing all lines.
f.read([character number]) – read specific
characters. Without parameter, it will read all the content. The read will move
the reading pointer ahead. We can use f.tell() to get the current pointer
position.
3. File Write
When we need to write the content to the
file, we need to open the file as write or append mode
f.write(“string”) – write some string into
the file
f.writelines(string list) – write mulitple
lines into the file
4. File delete
We need to use the os module to delete the
file in operation system. To avoid deleting non-existing file, we need to check
if the file is there.
os.remove(‘file’) or os.unlink(‘file’) #delete the file from os
Sample code:
import os
import os
if os.path.exists(‘/var/tmp/file’) :
os.remove (‘/var/tmp/file’)
5. file copy/move
we need to use the shutil module to copy or
move the file in between OS. To avoid the source file is already existing, we
need to check the source file as well.
Sample code
import shutil
if os.path.exists(‘/var/tmp/file’) :
shutil.copyfile(‘/var/tmp/file’,’/var/tmp/file1’ ) #copy
file
if os.path.exists(‘/var/tmp/file’) :
shutil.move(‘/var/tmp/file’,’/var/tmp/file1’ ) #move
file
6. directory relate operations
os.mkdir(“dirpath”, mode=) #mkdir
os.makedirs(‘dirpath’, mode=) #create directory when the parent
directory is not existing
os.rmdir(‘directory’) #remove the directory
os.removedirs(‘directorytree’) #remove
the directory tree.
os.listdir(‘path’) #list the files and directories in the directory
(the name is a little bit confusing)
os.walk() or os.path.walk() # Traversal the directory.
os.walk() will
return a tuple, each element contains the path, subdirectories and files
7. stdin, stdout, stderr
we can change the stdin, stdout, stderr in
python by assign sys.[file] to other values
for example, we will change the stdout
>>> import sys
>>>
sys.stdout=open(r"./hello.txt","a") #change the stdout value
>>> print "good bye" # you won’t see
the ‘good bye’ printed onto screen.
>>> sys.stdout.close() # it is in the
hello.txt file
