How to run an EXE, with argument, capture output value

noydb noydb00 at
Thu Nov 18 23:54:23 CET 2010

On Nov 18, 5:22 pm, Tim Harig <user... at> wrote:
> On 2010-11-18, noydb <jenn.du... at> wrote:
> > import subprocess
> > pig = subprocess.Popen(["C:\Halls\hallbig2.exe"],
> > stdin=subprocess.PIPE, stdout=subprocess.PIPE)
> > result = pig.communicate(input='C:\Halls\Input\Ea39j.txt')[-1] #I need
> > to capture the, what I think is the, last output
> From the subprocess documentation:
>            [62]communicate() returns a tuple (stdoutdata, stderrdata).
>            Note that if you want to send data to the process's stdin,
>            you need to create the Popen object with stdin=PIPE. Similarly,
>            to get anything other than None in the result tuple, you need
>            to give stdout=PIPE and/or stderr=PIPE too.
> By using index [-1] you are accessing the processes stderr stream.  I am
> not really sure why you changed it.  It doesn't give you the last output.
> Index 0 gives you *all* of stdout and index 1 gives you *all* of stderr,
> period.  If you wish to further disect the output to get say the last line,
> then you will need to parse it separately.

Okay, I see now.  I did run it to start with 0 -- still same result no
matter if 0 or -1.
So, what is result (stdout, using [0]) in this case?  (yes, i know I
sound dumb - programming is not my background, obviously).  A list,
tuple???  How do you access stdout (or is it stdoutdata?) results?  I
have tried, get errors with all attempts.  The exe gui returns several
statistical values uopn inputing a text file (containing numerous
lines of <value> <frequency>) and clicking compute - I want just one
of the values.

> > print result
> > print pig.returncode
> >>> None
> >>> 0
> > So the tuple is empty. ??  The exe executes fine and returns output in
> > th exe tool itself.  The python script seems to execute fine, no
> > errors, '...returned exit code 0'.  Any ideas/suggestions?
> No the tuple contains two items (stdout, stderr).  The first is what the
> program printed to its stdout stream (which is most likely the output you
> see if you run the command at a terminal/console).  The second is what it printed to its
> stderr stream which is a channel used for out of band data such as error or
> status messages.  In this case, it is None, because you did open stderr as a
> subprocess.PIPE.

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