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I would like to capture in a file the standard output by a child Process spawned by an external package.

I can NOT simply redirect sys.stdout to a file, as this does not capture the output of new processes (How can I capture the stdout output of a child process?).

But unfortunately, I also can NOT simply use subprocess or the terminal to capture stdout, since I am not spawning the process -- it is spawned by the code in an external Python package.

Specifically, I am using the API to the package pystan. Some of the functions in this package spawn child MCMC runs that write to standard output.

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Jesse Bloom
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1 Answers1

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I only see two ways to do this:

  • monkey-patch pystan (might take several patches)
  • monkey-patch subprocess (might get more info than you want)

I would go with the subprocess monkey-patch: write your own version of Popen (or whatever pystan is using, and replace the subprocess version with your own. Your version would track STDOUT and save it somewhere you could get at it.

Roughly, something like this:

import subprocess
original_Popen = subprocess.Popen

def my_Popen(..., stdout=PIPE, ...):  # or somesuch
    ...

subprocess.Popen = my_Popen

# call pystan here

subprocess.Popen = original_Popen # if needed
Ethan Furman
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