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user@test:~/learn/python$ pydoc -k zip
zipimport - zipimport provides support for importing Python modules from Zip archives.
gzip - Functions that read and write gzipped files.
lib2to3.fixes.fix_itertools - Fixer for itertools.(imap|ifilter|izip) --> (map|filter|zip) and
lib2to3.fixes.fix_itertools_imports - Fixer for imports of itertools.(imap|ifilter|izip|ifilterfalse)
lib2to3.fixes.fix_zip - Fixer that changes zip(seq0, seq1, ...) into list(zip(seq0, seq1, ...)
zipfile - Read and write ZIP files.
** (python2.7:2599): CRITICAL **: pyg_register_boxed: assertion `boxed_type != 0' failed
Segmentation fault (core dumped)
user@test:~/learn/python$ 
user@test:~/learn/python$ uname -a
Linux govinda 3.2.0-24-generic #39-Ubuntu SMP Mon May 21 16:52:17 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
user@test:~/learn/python$

This works fine for me. It is almost certain to be a case of something on your pythonpath crashing when pydoc imports it while looking for things that match the keyword. There is unfortunately no way to bullet proof pydoc against this.

Which version of Python 2.7.x are you running? If it is less than Python 2.7.3, this is likely a duplicate of Issue7425, the fix for which improved the robustness of pydoc -k as of 2.7.3.

Ned: since it is a core dump, I doubt the patch for ignoring exceptions during import will fix this. Note that 'pyg_register_boxed' is not a string that appears in the python source, so it is pretty certainly a third party extension module that is segfaulting the interpreter. 
The following ubuntu bug appears to be relevant: https://bugs.launchpad.net/ubuntu/+source/python2.7/+bug/896836 

Yeah, pydoc will walk and import all installed Python modules, which may trigger various kinds of issues with buggy third-party stuff.
Note that in 2.x, extension modules compiled with different fundamental options (such as debug/non-debug) aren't differentiated, which may the be cause of the present issue.