How can I redirect os.system() output in Python?

Question

I am trying to run something inside a Python file, and i do not want to see in the Python console the run output:

os.system("cd ../programs/{0} && ./run".format(project))

How can I do it? I tried with subprocess.call() but it does not compile.

What do you mean by "subprocess.call() but it does not compile"? Python isn't compiled and the subprocess module is a standard library. So what actually happens when you use it? Because I think using it is your answer right there. — Ted Klein Bergman, Mar 12 '20 at 17:46
Also, you aren't actually doing any redirection here. Where do you want to redirect output to? — Charles Duffy, Mar 12 '20 at 17:47
@TedKleinBergman Most Python implementations are indeed compiled, just not to native machine code. CPython compiles Python byte code (analogous to Java compiling to Java byte code). — chepner, Mar 12 '20 at 17:52
@chepner Yes, that's true. I meant more in the sense that you don't run a separate compilation step where compilations error and runtime errors are disjunct. In hindsight, this distinction is not necessary for the problem at hand. — Ted Klein Bergman, Mar 12 '20 at 17:57

score 3 · Answer 1 · edited Mar 12 '20 at 17:51

3

Redirecting stdout to /dev/null:

import subprocess

subprocess.call(['./run'],
                cwd=os.path.join('..', 'programs', project),
                stdout=subprocess.DEVNULL)

edited Mar 12 '20 at 17:51

ShadowRanger

answered Mar 12 '20 at 17:47

Charles Duffy

3

Also note: `os.path.join('..', 'programs', project)` would be a more canonical way of constructing the path. Or if you like modern Python tools more, `pathlib.Path('..', 'programs', project)`. – ShadowRanger Mar 12 '20 at 17:48
Huh, I never realized `subprocess` had added `DEVNULL`. – chepner Mar 12 '20 at 17:49
1

Also, `subprocess.run` is now recommended over `subprocess.call`. – chepner Mar 12 '20 at 17:51
I have tried to run the following: ``` subprocess.run(['./run'], cwd=pathlib.Path('..', 'programs', project), stdout=subprocess.DEVNULL) ``` – Enrique González Mar 14 '20 at 12:28
And i get the following error (I have copy only the last part of the error): ''' subprocess.run(['./run'], cwd=pathlib.Path('..', 'programs', project), stdout=subprocess.DEVNULL) File "/usr/lib/python3.6/subprocess.py", line 423, in run with Popen(*popenargs, **kwargs) as process: File "/usr/lib/python3.6/subprocess.py", line 729, in __init__ restore_signals, start_new_session) File "/usr/lib/python3.6/subprocess.py", line 1364, in _execute_child raise child_exception_type(errno_num, err_msg, err_filename) OSError: [Errno 8] Exec format error: './run' ''' – Enrique González Mar 14 '20 at 12:32
@EnriqueGonzález, that typically means your script doesn't have a shebang as its first line. Add one. (`#!/bin/sh` if it's written for POSIX sh, `#!/usr/bin/env bash` to choose the first versions of bash in the PATH, etc). – Charles Duffy Mar 14 '20 at 14:50

1 Answers1