We would need to introduce a new decorator so that classes overriding these methods can also make those methods "data descriptors", and so that users can define their own methods with this special behavior (this would be needed for __copy__, probably).
I have used this technique as a workaround in PyProtocols for __conform__ and __adapt__, so I know it works. In fact, here's the implementation:
def metamethod(func):
"""Wrapper for metaclass method that might be confused w/instance method"""
return property(lambda ob: func.__get__(ob,ob.__class__))
Basically, if I implement a non-slotted special method (like __copy__ or __getstate__) on a metaclass, I usually wrap it with this decorator in order to avoid the "metaconfusion" issue.
I didn't mention it because the technique had gotten somehow tagged in my brain as a temporary workaround until __conform__ and __adapt__ get slots of their own, rather than a general fix for metaconfusion. Also, I wrote the above when Python 2.2 was still pretty new, so its applicability was somewhat limited by the fact that 2.2 didn't allow super() to work with data descriptors. So, if you used it, you couldn't use super. This probably isn't a problem any more, although I'm still using the super-alike that I wrote as a workaround, so I don't know for sure. :)
PS. The term "data descriptor" now feels odd, perhaps we can say "hard descriptors" instead. Hard descriptors have a __set__ method in addition to a __get__ method (though the __set__ method may always raise an exception, to implement a read-only attribute).
I think I'd prefer "Override descriptor" to "Hard descriptor", but either is better than data descriptor. Presumably there will need to be backward compatibility macros in the C API, though for e.g. PyDescriptor_IsData or whatever it's currently called.
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