Live-output / stream from Python subprocess

Question

I am using Python and it's subprocess library to check output from calls using strace, something in the matter of:

subprocess.check_output(["strace", str(processname)]) 

However, this only gives me the output after the called subprocess already finished, which is very limiting for my use-case.

I need a kind of "stream" or live-output from the process, so I need to read the output while the process is still running instead of only after it finished.

Is there a convenient way to achieve this using the subprocess library? I'm thinking of a kind of poll every x seconds, but did not find any hints regarding on how to implement this in the documentation.

Many thanks in advance.

Answer 1

As of Python 3.2 (when context manager support was added to Popen), I have found this to be the most straightforward way to continuously stream output from a subprocess:

import subprocess


def run(args):
  with subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.STDOUT) as process:
    for line in process.stdout:
      print(line.decode('utf8'))