subprocess.Popen not creating a pipe

Andrew Parker gbofspam at
Sun Feb 1 15:00:36 EST 2009

On Sun, Feb 1, 2009 at 1:46 PM, Andrew Parker <gbofspam at> wrote:
> I'm having some fun with Popen.  I have the following line:
>    process = subprocess.Popen(command, stdout=subprocess.PIPE,
> stderr=subprocess.STDOUT)
>    print process.stdout
> Under normal circumstances, this displays:
>    <open file '<stdout>', mode 'w' at 0xb7f8e068>
> However, I have a binary that I use to kick off this script, and when
> that runs, it displays:
>    None
> So, two questions:
>    1.  What the heck is this binary doing that upsets Popen so much?
>    2.  What can *my script* do to get around this problem.
> Unfortunately I'm stuck using this binary, so its the python where I
> have to solve this.
> Any ideas?

so, tracing through subprocess.Popen, I see that os.pipe() is being
invoked for stdout.  This is returning (0, 3), and I assume the 0 is
conflicting with what python is assuming is stdin.  Calling pipe()
before Popen gets around my problem, as the pipe the Popen gets then
returns (4,5) which Popen seems happy with.

Sounds like a bug.  Should I report this, or is it expected/known behaviour?

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