[ python-Bugs-1531862 ] subprocess.Popen(cmd, stdout=sys.stdout) fails

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Bugs item #1531862, was opened at 2006-07-31 16:53
Message generated for change (Settings changed) made by niemeyer
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Category: Python Library
Group: Python 2.5
Status: Open
Resolution: None
Priority: 5
Submitted By: John A Meinel (jfmeinel)
>Assigned to: Gustavo Niemeyer (niemeyer)
Summary: subprocess.Popen(cmd, stdout=sys.stdout) fails

Initial Comment:
I'm currently using subprocess.Popen() to run a
command, and I allow the caller to specify where the
output should go.

One valid output is to send it to sys.stdout (fileno == 1)

The subprocess module seems to unconditionally close
stdout if a file handle is passed (even if it stdout).

Compare:
python -c "import subprocess,sys; \
  subprocess.Popen(['echo', 'hello'])"

versus
python -c "import subprocess,sys; \
  subprocess.Popen(['echo', 'hello'], stdout=sys.stdout)"

or even
python -c "import subprocess,sys; \
  subprocess.Popen(['echo', 'hello'], stdout=1)"

The first one prints 'hello' as expected.

The latter two give an error:
echo: write error: Bad file descriptor

Attached is a possible patch to subprocess.py

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Comment By: Anthony Baxter (anthonybaxter)
Date: 2006-08-16 04:16

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Making it check for particular FD numbers is a bad idea.
Instead, it should check that any FD that's being closed
isn't in the set
(sys.stdin.fileno(), sys.stdout.fileno(), sys.stderr.fileno()) 




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Comment By: Neal Norwitz (nnorwitz)
Date: 2006-08-16 04:11

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If stderr == stdout, this patch won't fix that, will it? 
Shouldn't you add 1, 2 to the blacklist for stderr?  (The
patch adds 2, I think 1 may also be required.)

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