python call external program non-blocking way

Question

is there a way to call an external program inside python and don't wait for its execution to finish?

I tried this, but no luck:

os.system("external_program &")

Normally, if I call external_program & inside a bash shell it executes as a background process. How can I do it inside python? For, my special case, creating another thread does not work. After main python scrip is done, the external program should continue its execution.

Can you run it in parallel? There are no dependencies?

Raphael
– Raphael

2019-11-09 00:20:48 +00:00
Commented Nov 9, 2019 at 0:20 — Raphael
– Raphael, Commented Nov 9, 2019 at 0:20

Adam Rosenfield · Accepted Answer · 2013-06-07 14:38:30Z

5

Yes, use the subprocess module. For example:

p = subprocess.Popen(['external_program', 'arg1', 'arg2']) # Process is now running in the background, do other stuff... ... # Check if process has completed if p.poll() is not None: ... ... # Wait for process to complete p.wait()

edited Jun 7, 2013 at 14:38

answered Jun 7, 2013 at 14:37

Adam Rosenfield

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5 Comments

Gokhan Ka Over a year ago

I tried this. It is still blocking. And, if it works, what happens if I don't wait at the end? Is it going to be killed?

Gokhan Ka Over a year ago

I realized that it actually works but the main script waits at the end. I need a complete independence from the main script. Is it possible?

Adam Rosenfield Over a year ago

@GokhanKa: If you don't want the main script to wait, then don't call wait(), it's that simple. If you exit while the subprocess is still running, it will continue to run in the background.

Gokhan Ka Over a year ago

I'm not calling wait(). It does not even execute sys.exit(0) after Popen call. If I call p.terminate(), it immediately terminates the subprocess and exits. How strange is this?

tripleee Over a year ago

Coming from a duplicate, I want to emphasize: replace os.system("thing &") with p = subprocess.Popen(['thing']) without the & (and without the shell) and do whatever else you want to do. p will exist and be running in the background because you created a subprocess, just like the shell does with & and you can eventually reap it with p.wait(). Things will be a little more complex and subtle if thing blocks because it is writing to a pipe or something, but there are other questions which explain this in more detail.

glglgl · Accepted Answer · 2013-06-07 14:37:30Z

Forget about os.system(). It is deprecated in favour of the subprocess module.

It provides a way to execute subprograms for almost every thinkable use case.

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