Disable console output from subprocess.Popen in Python

Question

I run Python 2.5 on Windows, and somewhere in the code I have

subprocess.Popen("taskkill /PID " + str(p.pid))

to kill IE window by pid. The problem is that without setting up piping in Popen I still get output to console - SUCCESS: The process with PID 2068 has been terminated. I debugged it to CreateProcess in subprocess.py, but can't go from there.

Anyone knows how to disable this?

What is the problem with subprocess.Popen("taskkill /PID " + str(p.pid) + " > NUL")? — Svetlozar Angelov, Aug 07 '09 at 13:50
Maybe because python runs on Windows? It says that '>' is not a valid option of taskkill command — Denis Masyukov, Aug 07 '09 at 14:12
I tried that first, for some reason it doesn't parse correctly. >>> ERROR: Invalid Argument/Option - '>'. Type "TASKKILL /?" for usage. That works on the cmd line though. — Mark, Aug 07 '09 at 14:14

Alice Purcell · Answer 1 · 2023-02-03T08:07:51.627

from subprocess import check_call, DEVNULL, STDOUT

check_call(
    ("taskkill", "/PID", str(p.pid)),
    stdout=DEVNULL,
    stderr=STDOUT,
)

I always pass in tuples (or lists) to subprocess as it saves me worrying about escaping. check_call ensures (a) the subprocess has finished before the pipe closes, and (b) a failure in the called process is not ignored.

If you're stuck in python 2, subprocess doesn't provide DEVNULL. However, you can replicate it by opening os.devnull (the standard, cross-platform way of saying NUL in Python 2.4+):

import os
from subprocess import check_call, STDOUT

DEVNULL = open(os.devnull, 'wb')
try:
    check_call(
        ("taskkill", "/PID", str(p.pid)),
        stdout=DEVNULL,
        stderr=STDOUT,
    )
finally:
    DEVNULL.close()

Mark · Accepted Answer · 2009-08-07T13:48:21.483

11

fh = open("NUL","w")
subprocess.Popen("taskkill /PID " + str(p.pid), stdout = fh, stderr = fh)
fh.close()

edited Aug 07 '09 at 13:48

answered Aug 07 '09 at 13:41

Mark

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Thank you! This piece actually works. I completely forgot about NUL. – Denis Masyukov Aug 07 '09 at 14:12
3

I think there's a race condition there — you may close the pipe before your subprocess has finished and cause it to terminate early. – Alice Purcell Aug 07 '09 at 20:01
@chrispy - you're correct, I think there should be a .communicate() in there – orip Nov 08 '09 at 12:26
@chrispy,@orip: actually, isn't the answer to add `.wait()` to the subprocess line? – Harvey Dec 29 '10 at 22:07
Just a silly question: I want to do the exact same thing, and I don't understand why stdout=None prevent the thread to display stuff... – nbarraille Jul 16 '11 at 21:28
5

You can better use: os.devnull instead of "NUL", because that is cross-platform. Windows uses: 'nul' and Linux uses: '/dev/null'. – Melroy van den Berg Feb 13 '14 at 21:17

Disable console output from subprocess.Popen in Python

2 Answers2