Popen3 and capturestderr
pronovic at skyjammer.com
Wed Mar 9 19:06:29 CET 2005
On Wed, Mar 09, 2005 at 06:17:50AM -0000, Donn Cave wrote:
> Quoth Kenneth Pronovici <pronovic at skyjammer.com>:
> | If ignoreStderr=False, I use popen2.Popen4 so that stderr and stdout are
> | intermingled. If ignoreStderr=True, I use popen2.Popen3 with
> | capturestderr=True so stderr doesn't appear in the output. This
> | functionality exists so I have an equivalent of command-line redirection
> | of stderr, i.e. command 2>/dev/null.
> | After some digging, I've decided that this behavior probably occurs
> | because I am ignoring the pipe.childerr file object. Indeed, if I call
> | pipe.childerr.close() right after opening the pipe, my "ls" command that
> | had been hanging completes normally. However, other commands which
> | actually attempt to write to stderr don't seem to like this very much.
> | What is the right way to discard stderr when working with a pipe? I
> | want to consistently throw it away, and I don't see a good way to do
> | this with the popen2 implementation.
> Right, popen2 gives you about 3 options, out of probably dozens that
> you could get with shell redirections. On the other hand, the source
> is available, and Python is an OOP language, so I assume there is no
> reason you can't make a derived class that does just what you want.
> In the present case I guess that would mean something like
> null = os.open('/dev/null', os.O_RDWR)
> os.dup2(null, 0)
> os.dup2(null, 2) (depending)
> along with other stuff you can just copy from Popen4.
Ah... ok, subclassing is an option I hadn't considered. I'll give that
a whirl and see whether I can make it work.
Kenneth J. Pronovici <pronovic at ieee.org>
Personal Homepage: http://www.skyjammer.com/~pronovic/
"They that can give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
- Benjamin Franklin, Historical Review of Pennsylvania, 1759
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