Python – How to run an external command asynchronously from Python


I need to run a shell command asynchronously from a Python script. By this I mean that I want my Python script to continue running while the external command goes off and does whatever it needs to do.

I read this post:

Calling an external command in Python

I then went off and did some testing, and it looks like os.system() will do the job provided that I use & at the end of the command so that I don't have to wait for it to return. What I am wondering is if this is the proper way to accomplish such a thing? I tried but it will not work for me because it blocks on the external command.

Please let me know if using os.system() for this is advisable or if I should try some other route.

Best Solution

subprocess.Popen does exactly what you want.

from subprocess import Popen
p = Popen(['watch', 'ls']) # something long running
# ... do other stuff while subprocess is running

(Edit to complete the answer from comments)

The Popen instance can do various other things like you can poll() it to see if it is still running, and you can communicate() with it to send it data on stdin, and wait for it to terminate.