subprocess -popen - reading stdout from child - hangs

gregpinero at gmail.com gregpinero at gmail.com
Sun Sep 23 06:16:43 CEST 2007


On Sep 22, 11:28 pm, "gregpin... at gmail.com" <gregpin... at gmail.com>
wrote:
> Let's say I have this Python file called loop.py:
>
> import sys
> print 'hi'
> sys.stdout.flush()
> while 1:
>     pass
>
> And I want to call it from another Python process and read the value
> 'hi'.  How would I do it?
>
> So far I have tried this:
>
> >>> proc = subprocess.Popen('python /home/chiefinnovator/loop.py',shell=True,stdin=subprocess.PIPE,stdout=subprocess.PIPE)
> >>> proc.stdout.read()
>
> But it just hangs at read()
>
> proc.communicate() also just hangs.  What am I doing wrong?  Please
> advise.

Well, using this subclass of subprocess.Popen fixes the problem
(http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/440554)

I don't understand how it works though.  Would anyone mind
explaining?  I'm thinking there's something fundamental about Unix
processes I'm not understanding.

-Greg




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