This module is used for dealing with external commands, intended to be a replacement to the old

os.system and the like.

The subprocess module allows us to spawn processes, connect to their input/output/error pipes, and obtain their return codes

subprocess.call()

shell is set to flase default

import subprocess
ls_output = subprocess.check_output(['ls'])
subprocess.check_output(['ls', '-l'])

Subprocess can also run command-line instructions via a shell program. 
This is usually dash/bash on Linux and cmd on windows.

subprocess.call('ls | wc -l', shell=True)

Input and Output

Return Codes

You can use subprocess.call return codes to determine the success of the command.

Every process will return an exit code and you can do something with your script

based on that code.

If the return code is anything else than zero, it means that an error occurred.

stdin, stdout and stderr

One of the trickiest part I had with subprocess was how to work with pipes

and to pipe commands together.

PIPE indicates that a new pipe to the child should be created.

The default setting is "None", which means that no redirection will occur.

The standard error (or stderr) can be STDOUT, which indicates that the stderr data from the child process should be captured into the same file handle as for stdout.

Redirecting stdout to “nothing” in python, print will show nothing

Cross-platform:

import os
import sys
f = open(os.devnull, 'w')
sys.stdout = f

On Windows:

f = open('nul', 'w')
sys.stdout = f

On Linux:

f = open('/dev/null', 'w')
sys.stdout = f

examples : ping program

import subprocess as sub

p1 = sub.call('ping -c  %s) %ip , shell =True,stderr = sub.STDOUT) 
if p1 == 0 :
  print "the server %s is alive'%ip
  return ret

import subprocess as sub

ret = sub.Popen('uname -sv', shell =True, stdout = sub.PIPE)
uname = ret.stdout.read().strip()
print (unmae)
 'Linux #1 SMP Tue Feb 12 02:46:46 UTC 2008'