os.popen does not seem to catch stdout

gregpinero at gmail.com gregpinero at gmail.com
Wed Nov 7 19:17:54 CET 2007


On Nov 7, 11:31 am, kyoso... at gmail.com wrote:
> On Nov 7, 7:58 am, zane.selv... at gmail.com wrote:
>
>
>
> > Hi there,
>
> > I've been banging my head against this for a day, and I can't take it
> > anymore.  It's probably a stupid error, but I don't see where.
>
> > I'm trying to use Python to call an external program, and then catch
> > and process the output of that program.  Seems simple enough.  The
> > command I'm trying to run, in the test, is:
>
> > "/Users/zane/svn/stress/satstress/satstress -r1.561e+06 -a5 -s45000 -
> > e0 -R6.709e+08 -g1.31472 -m1.8987e+27 -Q57100.1 -n0.333355 -Y9.29881e
> > +09 -k1e+22 -Z1.19173 -z-6.293e-05 -V0.309434 -v-2.903e-05 -W1.81305 -
> > w-0.00418645 -U0.474847 -u-0.00276624 -C /tmp/18_tmp.gen -b 60"
>
> > When I run it at my zsh prompt, I get the expected output.
>
> > If I let ss_cmd equal the above string within ipython (or the standard
> > python interactive interpreter):
>
> > ss_outlines = os.popen(ss_cmd).readlines()
>
> > ss_outlines contains the same output I saw when I ran the command at
> > my zsh prompt, one line per list element, as expected.
>
> > However, when I try doing the same thing from within a program, it
> > fails.  ss_outlines is an empty list.
>
> > I've tried using subprocess.Popen(), and subprocess.call(), and
> > subprocess.check_call(), and all have yielded similar results.  I did
> > find, however, that the return value python is getting from the
> > program I'm calling is different from what I get at the command line
> > (I get 0, python gets -11).
>
> > Does this ring a bell for anyone?
>
> > I'm using Python 2.5.1 on a Mac running OS X 10.5.
>
> I think when you use subprocess.Popen, you need to do something set
> the shell to True to get it to behave like running from a command
> prompt:
>
> subprocess.Popen('some command', shell=True)
>
> Seehttp://docs.python.org/lib/node529.htmlfor more details.
>
> You'll also find a fairly interesting thread on this topic here:
>
> http://mail.python.org/pipermail/chicago/2005-November/000141.htmlhttp://mail.python.org/pipermail/python-list/2005-October/347508.html
>
> This seems to be a recipe on it:
>
> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/440554
>
> Mike


That's right, and I think you also want to put the whole command in a
list or tuple, one item for each arg.  I don't know why though.

-Greg




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