Using module 'subprocess' with timeout

Question

Here's the Python code to run an arbitrary command returning its stdout data, or raise an exception on non-zero exit codes:

proc = subprocess.Popen(

    cmd,

    stderr=subprocess.STDOUT,  # Merge stdout and stderr

    stdout=subprocess.PIPE,

    shell=True)

communicate is used to wait for the process to exit:

stdoutdata, stderrdata = proc.communicate()

stdoutdata, stderrdata = proc.communicate()

The subprocess module does not support timeout--ability to kill a process running for more than X number of seconds--therefore, communicate may take forever to run.

What is the simplest way to implement timeouts in a Python program meant to run on Windows and Linux?

Answer 1

In Python 3.3+:

from subprocess import STDOUT, check_output

output = check_output(cmd, stderr=STDOUT, timeout=seconds)

output is a byte string that contains command's merged stdout, stderr data.

This code raises CalledProcessError on non-zero exit status as specified in the question's text unlike proc.communicate() method.

I've removed shell=True because it is often used unnecessarily. You can always add it back if cmd indeed requires it. If you add shell=True i.e., if the child process spawns its own descendants; check_output() can return much later than the timeout indicates, see Subprocess timeout failure.

The timeout feature is available on Python 2.x via the subprocess32 backport of the 3.2+ subprocess module.