[Python-Dev] Exceptions *must*? be old-style classes?

[Guido van Rossum]

[Armin]
> For reference, PyPy doesn't have old-style classes at all so far, so we had to
> come up with something about exceptions.  After some feedback from python-dev
> it appears that the following scheme works reasonably well.  Actually it's
> surprizing how little problems we actually encountered by removing the
> old-/new-style distinction (particularly when compared with the extremely
> obscure workarounds we had to go through in PyPy itself, e.g. precisely
> because we wanted exceptions that are member of some (new-style) class
> hierarchy).
> 
> Because a bit of Python code tells more than long and verbose explanations,
> here it is:
> 
> def app_normalize_exception(etype, value, tb):
[...]
>     elif type(etype) is str:
>         # XXX warn -- deprecated
>         if value is not None and type(value) is not str:
>             raise TypeError("string exceptions can only have a string value")

That is stricter than classic Python though -- it allows the value to
be anything (and you get the value back unadorned in the except 's',
x: clause).

[Michael]
> It would still be worth doing, IMHO.

Then let's do it. Care to resurrect your patch? (And yes, classic
classes should also be allowed for b/w compatibility.)

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)