CODEWITHSUNDEEP
pythonpython-2.7subprocess
SuperBiasedMan
SuperBiasedMan

Reputation: 9969

Start another program and leave it running when the script ends

I'm using subprocess.Popen to launch an external program with arguments, but when I've opened it the script is hanging, waiting for the program to finish and if I close the script the program immediately quits.

I thought I was just using a similar process before without issue, so I'm unsure if I've actually done it wrong or I'm misremembering what Popen can do. This is how I'm calling my command:

    subprocess.Popen(["rv", rvFile, '-nc'])
    raw_input("= Opened file")

The raw_input part is only there so the user has a chance to see the message and know that the file should be opened now. But what I end up getting is all the information that the process itself is spitting back out as if it were called in the command line directly. My understanding was that Popen made it an independent child process that would allow me to close the script and leave the other process open.

The linked duplicate question does have a useful answer for my purposes, though it's still not working as I want it.

This is the answer. And this is how I changed my code:

DETACHED_PROCESS = 0x00000008
pid = subprocess.Popen(["rv", rvFile, '-nc'], creationflags=DETACHED_PROCESS).pid
raw_input("= Opened file")

It works from IDLE but not when I run the py file through the command prompt style interface. It's still tied to that window, printing the output and quitting the program as soon as I've run the script.

Upvotes: 3

Views: 6083

Answers (3)

SuperBiasedMan
SuperBiasedMan

Reputation: 9969

This is specifically for running the python script as a commandline process, but I eventually got this working by combining two answers that people suggested.

Using the combination of DETACHED_PROCESS suggested in this answer worked for running it through IDLE, but the commandline interface. But using shell=True (as ajsp suggested) and the DETACHED_PROCESS parameter it allows me to close the python script window and leave the other program still running.

DETACHED_PROCESS = 0x00000008
pid = subprocess.Popen(["rv", rvFile, '-nc'], creationflags=DETACHED_PROCESS, shell=True).pid
raw_input("= Opened file")

Upvotes: 0

ajsp
ajsp

Reputation: 2670

Sorry for such a short answer but I have not earned enough points to leave comments yet. Anyhow, put the raw_input("= Opened file") inside the file you are actually opening, rather than the program you are opening it from.

If the file you are opening is not a python file, then it will close upon finishing,regardless of what you declare from within python. If that is the case you could always try detaching it from it's parent using:

from subprocess import Popen, CREATE_NEW_PROCESS_GROUP
subprocess.Popen(["rv", rvFile, '-nc'], close_fds = True | CREATE_NEW_PROCESS_GROUP)

Upvotes: 1

Matt Seymour
Matt Seymour

Reputation: 9395

The stackoverflow question Calling an external command in python has a lot of useful answers which are related.

Take a look at os.spawnl, it can take a number of mode flags which include NOWAIT, WAIT.

import os
os.spawnl(os.P_NOWAIT, 'some command')

The NOWAIT option will return the process ID of the spawned task.

Upvotes: 2

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