[Python-Dev] metaclass insanity

30 Oct 2002 18:17:26 +0000

Guido van Rossum <guido@python.org> writes:
> > I guess one way of doing this would be to reimplement mro resolution
> > and so on in Python, which would be annoying and inefficient. Hmm.
>> Alas, yes. You'd have to be able to write a class's tp_mro slot
> (corresponding to the __mro__ attribute), but there's no way to do
> that in Python, because it is too easy to cause mistakes. E.g. all
> C code that currently uses tp_mro assumes that it is a tuple whose
> items are either types or classic classes.
>> The best thing to do would perhaps to make __mro__ assignable, but
> with a check that ensures the above constraint. I think I'd take a
> patch for that.

Shouldn't be too hard.
> I'd also take a patch for assignable __bases__. Note that there are
> constraints between __bases__ and __base__.

Should assigning to __bases__ automatically tweak __mro__ and
__base__? Guess so. What would assigning to __base__ do in isolation?
Perhaps that shouldn't be writeable.
> I'd also take a patch for assignable __name__.

This is practically a one-liner, isn't it? Not hard, anyway.
And there was me wondering what I was going to do this evening.
Cheers,
M.
-- 
 Now this is what I don't get. Nobody said absolutely anything
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