[ python-Bugs-1736483 ] os.popen('yes | echo hello') stuck

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Bugs item #1736483, was opened at 2007-06-13 13:41
Message generated for change (Comment added) made by cpegeric
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Category: Python Library
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Eric (cpegeric)
Assigned to: Nobody/Anonymous (nobody)
Summary: os.popen('yes | echo hello') stuck

Initial Comment:
after calling os.popen('yes | echo hello'), the process never returns.

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>Comment By: Eric (cpegeric)
Date: 2007-06-14 03:49

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It works now. thank you.

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Comment By: Ilguiz Latypov (ilgiz)
Date: 2007-06-14 03:22

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The SIG_DFL default handler seems to terminate the current process
(argument to popen()), not Python script.


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Comment By: Ilguiz Latypov (ilgiz)
Date: 2007-06-14 03:15

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It appears your "yes" does not catch SIGPIPE.  I've reproduced the issue
with

$ python -c 'import sys, os; sys.stdout.write(os.popen("while :; do echo
yes ; done | echo hello").read())'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
KeyboardInterrupt

The documentation on Python module signal says SIGPIPE is ignored by
Python as well.  My work-around to this was to catch SIGPIPE, but the GNU C
library would terminate the whole script.

$ python -c 'import sys, os, signal; signal.signal(signal.SIGPIPE,
signal.SIG_DFL); sys.stdout.write(os.popen("while :; do echo yes ; done |
echo hello").read())'
hello

http://www.gnu.org/software/libc/manual/html_node/Operation-Error-Signals.html

Perhaps, writing own signal handler might help.


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Comment By: Eric (cpegeric)
Date: 2007-06-14 02:46

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sorry for the misunderstanding.

Here is the result. 

% yes | echo hello
hello
% echo $?
0
%

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Comment By: Ilguiz Latypov (ilgiz)
Date: 2007-06-14 02:24

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I've realized my suggestion was not precise.  I meant asking to run the
argument to popen() rather than popen().

That is, I would run this from command line to see if there is an issue
with the shell:

$ yes | echo hello



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Comment By: Eric (cpegeric)
Date: 2007-06-14 01:28

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command line also get stuck.  The OS is MacOSX.  Python version 2.3.5. 
Will it help update to new version?

I quited the program by Ctrl-C.

 python -c 'import sys, os; sys.stdout.write(os.popen("yes | echo
hello").read())'
^CTraceback (most recent call last):
  File "<string>", line 1, in ?
KeyboardInterrupt



% python -c 'import sys, os; sys.stdout.write(os.popen3("yes | echo
hello")[1].read())'
^CTraceback (most recent call last):
  File "<string>", line 1, in ?
KeyboardInterrupt



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Comment By: Ilguiz Latypov (ilgiz)
Date: 2007-06-13 17:07

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Could you try the same command from your shell?

I am guessing "yes" will write an error message about the broken pipe to
stderr.

$ python -c 'import sys, os; sys.stdout.write(os.popen("yes | echo
hello").read())'
yes: standard output: Broken pipe
yes: write error
hello

$ python -c 'import sys, os; sys.stdout.write(os.popen3("yes | echo
hello")[1].read())'
hello


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