pl/python validator function - Mailing list pgsql-hackers

Here's a patch implementing a validator functoin mentioned in
http://archives.postgresql.org/pgsql-hackers/2010-12/msg01991.php. It's
an incremental patch on top of the plpython-refactor patch sent eariler.

Git branch for this patch:
https://github.com/wulczer/postgres/tree/validator.

Cheers,
Jan