From: Martin v. Loewis <martin@v.loewis.de>
Guido van Rossum <guido@python.org> writes:
What does "that" (in "If that is the rule") refer back to?
"user-defined exceptions be derived from Exception". It is only a recommendation in the sense that you can use arbitrary classic classes. If the rule is eventually tightened, it is ok if new-style classes are not allowed as exceptions right now. An action is only needed if you pronounce that it is desirable to allow new-style classes as exceptions - which would necessarily have a base class that is not derived from Exception.
But this is legal in 2.2
class Z(str,Exception): ... pass ... Z.__bases__ (<type 'str'>, <class exceptions.Exception at 0x00757700>) Z.__base__ <type 'str'>
so the issue is more subtle or I'm missing something? regards.