Proper way to close a file object used as stdout argument for Popen

Question

In my script, I redirect stdout to a file as below:

with open(logFileName, 'w') as fp:
  proc = Popen([myexe], stdout=fp)
  # proc.wait() # I don't want to block until process completes.

I understand that the fp would be closed even before the process completes. Thus my program does not work as expected.

If I do a wait(), it will work but I don't want to block.

I am wondering what is the right way to do this. Is a separate thread the only way? Surprisingly, I could not find an answer through google through this requirement should be a very common one.

Update: I see that it was not working for a different reason. It works fine even though the file object would be closed even before the process completes. Still not sure if this is right way to do.

Just do not use a `with` statement? – Stop harming Monica Jan 25 '18 at 14:05 — Stop harming Monica, Jan 25 '18 at 14:05

score 1 · Answer 1 · answered Jan 25 '18 at 13:44

1

use subprocess:

import subprocess

with open(logFileName, 'w') as fp:
    p = subprocess.Popen( [myexec], stdout=subprocess.PIPE, stderr=subprocess.PIPE )
    fp, error_msg = p.communicate()

answered Jan 25 '18 at 13:44

Nemelis

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I don't want to block until the process terminates. Do I need to look into threads? – Suresh Jan 25 '18 at 13:48
See the answer on my question in https://stackoverflow.com/questions/34314475/how-to-make-subprocess-only-communicate-error – Nemelis Jan 25 '18 at 14:36

Proper way to close a file object used as stdout argument for Popen

1 Answers1