python execute shell command and continue without waiting and check if running before executing

Question

I need to execute two other python scripts from another one. commands look like this:

# python send.py

# python wait.py

This will happen in a loop that will sleep for 1 minute then re-run.

Before executing the commands to start the other scripts I need to make sure they are not still running.

Why can't you import the two scripts and call the functions inside of them normally? — Blender
– Blender, Commented Sep 26, 2012 at 15:31
Because the two apps will be rewritten in a different language at some point. — transilvlad
– transilvlad, Commented Sep 26, 2012 at 15:34
subprocess seems to wait for the application to finish before continuing. I need to just execute and move on. — transilvlad
– transilvlad, Commented Sep 26, 2012 at 15:37

amirouche · Accepted Answer · 2012-09-26 15:45:18Z

21

You can use subprocess.Popen to do that, example:

import subprocess

command1 = subprocess.Popen(['command1', 'args1', 'arg2'])
command2 = subprocess.Popen(['command2', 'args1', 'arg2'])

if you need to retrieve the output do the following:

command1.wait()
print command1.stdout

Example run:

sleep = subprocess.Popen(['sleep', '60'])
sleep.wait()
print sleep.stdout  # sleep outputs nothing but...
print sleep.returncode  # you get the exit value

answered Sep 26, 2012 at 15:45

amirouche

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1 Comment

Fred Foo Over a year ago

stdout is only meaningful when stdout=subprocess.PIPE is passed to the Popen constructor.

transilvlad · Accepted Answer · 2012-09-26 16:50:58Z

import time
import commands
from subprocess import Popen

while True:
  t_ph = commands.getstatusoutput('ps -eo pid,args | grep script1.py | grep -v service | grep -v init.d | grep -v grep | cut -c1-6')
  t_fb = commands.getstatusoutput('ps -eo pid,args | grep script2.py | grep -v service | grep -v init.d | grep -v grep | cut -c1-6')

  if t_ph[1] == '':
    r_ph = Popen(["python", "script1.py"])

  if t_fb[1] == '':
    r_fb = Popen(["python", "script2.py"])

  time.sleep(60)

or

import time
import commands
from subprocess import Popen

r_ph = False
r_fb = False

while True:

  if r_ph == False:
    r_ph = Popen(["python", "script1.py"])
  else:
    if r_ph.poll():
      r_ph = Popen(["python", "script1.py"])

  if r_fb == False:
    r_fb = Popen(["python", "script2.py"])
  else:
    if r_fb.poll():
      r_fb = Popen(["python", "script2.py"])

  time.sleep(60)

this could be written a bit better but it works

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