[Armin]
> > ... is that the __adapt__() and __conform__() methods should work just
> > like all other special methods for new-style classes. The confusion
> > comes from the fact that the reference implementation doesn't do that.
> > It should be fixed by replacing:
> >
> > conform = getattr(type(obj), '__conform__', None)
> >
> > with:
> >
> > for basecls in type(obj).__mro__:
> > if '__conform__' in basecls.__dict__:
> > conform = basecls.__dict__['__conform__']
> > break
> > else:
> > # not found
> >
> > and the same for '__adapt__'.
> >
> > The point about tp_xxx slots is that when implemented in C with slots, you
> > get
> > the latter (correct) effect for free. This is how metaconfusion is avoided
> > in
> > post-2.2 Python. Using getattr() for that is essentially broken. Trying to
> > call the method and catching TypeErrors seems pretty fragile -- e.g. if you
> > are calling a __conform__() which is implemented in C you won't get a Python
> > frame in the traceback either.
[Thomas]
> I'm confused. Do you mean that
>
> getattr(obj, "somemethod")(...)
>
> does something different than
>
> obj.somemethod(...)
>
> with new style class instances? Doesn't getattr search the __dict__'s
> along the __mro__ list?
No, he's referring to the (perhaps not widely advertised) fact that
obj[X]
is not quite the same as
obj.__getitem__(X)
since the explicit method invocation will find
obj.__dict__["__getitem__"] if it exists but the operator syntax will
start the search with obj.__class__.__dict__.
--
--Guido van Rossum (home page: http://www.python.org/~guido/)
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