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telnetlib uses select.select. This limits it to being able to work when file descriptors are still below FD_SETSIZE (often 1024) meaning it can't be used in some large programs today.
It should use poll.
(it is probably easy to fix this and the telnetlib EINTR issue1049450 at the same time)

See also issue #10527, dealing with multiprocessing.
Note that this probably affects other modules besides telnetlib, so it might be interesting to find a way to factorize code (i.e. use poll() if available or fallback to select()).

Out of curiosity, are you reporting this because you ran into it in your code? I was not aware that telnet was still in real use.

> Note that this probably affects other modules besides telnetlib, so it 
> might be interesting to find a way to factorize code (i.e. use poll()
> if available or fallback to select()).
asyncore might have been the answer.

Éric: there are devices that still only allow telnet. Older cisco routers (*many* of which are still in the field) are just one example I'm familiar with. I don't currently have any tools that use telnetlib to talk to them, but I've got at least two I'd like to find time to write...and I can easily imagine this limitation coming up as a real issue at Google :)

Hi,
telnet.read_until() and telnet.expect() will use select.poll() instead of select.select() on systems where poll() is available.
The patch also includes updates to test_telnetlib, the read_until() tests were changed to test the case where poll() is unavailable. We also added unit tests for expect(), these are a copy of the read_until() tests.
This patch is against 2.7.
Akintayo

Is my approach ok or is the plan to follow neologix's suggestion and make one fix that works for all the select.select issues.

I think your approach is fine.
BTW for anyone who wants to chase the larger idea of dealing with all select.select use, take a look at the prototype for a select.select() implemented using poll.poll() that I just put in http://bugs.python.org/issue15032.

looking at this now. 2.7 commit first; then i'll forward port to 3.2/3.3.

New changeset c53e3aacb816 by Gregory P. Smith in branch '2.7':
Fixes Issue #14635: telnetlib will use poll() rather than select() when possible
http://hg.python.org/cpython/rev/c53e3aacb816 

New changeset de229dde486b by Gregory P. Smith in branch '3.2':
Fixes Issue #14635: telnetlib will use poll() rather than select() when possible
http://hg.python.org/cpython/rev/de229dde486b
New changeset 558e5ed678c3 by Gregory P. Smith in branch 'default':
Fixes Issue #14635: telnetlib will use poll() rather than select() when possible
http://hg.python.org/cpython/rev/558e5ed678c3 

This broke the buildbots without poll() (Windows).

Those should all be fixed as of my most recent commit.

New changeset d61e8050b7d7 by Gregory P. Smith in branch '2.7':
Fixes Issue #17200: telnetlib's read_until and expect timeout was broken by the
http://hg.python.org/cpython/rev/d61e8050b7d7
New changeset 46186736e91c by Gregory P. Smith in branch '3.3':
Fixes Issue #17200: telnetlib's read_until and expect timeout was broken by the
http://hg.python.org/cpython/rev/46186736e91c