[Python-Dev] metaclass insanity

[Michael Hudson]

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
  bad about anything.  Yet it is always possible to just pull
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