Injecting into database exceptions is more portable than copying exceptions

[ianb@…]

In django.core.db.init exceptions like DatabaseError are copied in from "the" database. This means only one database backend can be supported at any one time.

An alternate way to handle this is to inject a superclass into the database exceptions. sqlapi.exceptions is an example of this technique: ​http://svn.sqlobject.org/sqlapi/trunk/sqlapi/exceptions.py

[Malcolm Tredinnick]

The only thing preventing me from saying this is a really good idea is whether it's sensible Python practice. Somebody (me?!) needs to do some research about whether injecting extra base classes like this is frowned on. I suspect it won't work in general (e.g. C-wrapped classes), but I don't know.

If we can guarantee it works for all database exceptions, then it's a good idea.

[Malcolm Tredinnick]

We can't use this. It is not possible to assign to __bases__ in new-style classes, every exception class should be derived from Exception and in Python 2.5, Exception became a new-style class. So the method touted in the above link won't work in 2.5.