Comment 9 for bug 1170063

@niemeyer: I think you're right; in at least some places psycopg2 definitely creates its errors directly from C without fetching the class from the Python namespace.

I spent some time thinking about this today, because it would be worthwhile for Launchpad to start using PostgreSQL's json type (see https://code.launchpad.net/~cjwatson/launchpad/db-distroseries-publishing-options/+merge/278241), but psycopg2 only added support for adapting that in 2.5, which causes us to run into this bug. It occurred to me that we could use the isinstance/issubclass customisation added in Python 2.6 for abc.ABCMeta, and I later noticed https://bugs.launchpad.net/storm/+bug/1006711 which suggests the same thing. Could you review https://code.launchpad.net/~cjwatson/storm/psycopg-2.5/+merge/278330 which implements this?