Strange metaclass behaviour
michele.simionato at gmail.com
Thu Mar 23 15:57:52 CET 2006
Ziga Seilnacht wrote:
> - Since D does not have a __metaclass__ attribute,
> its type is determined from its bases.
> - Since A is the first base, its type (M_A) is called;
> unfortunately this is not the way metaclasses are
> supposed to work; the most derived metaclass should
> be selected.
> - M_A's __new__ method calls the __new__ method of the
> next class in MRO; that is, super(M_1, meta).__new__
> is equal to type.__new__.
> - In type.__new__, it is determined that M_A is not
> the best type for D class; it should be actually M_B.
> - Since type.__new__ was called with wrong metaclass
> as the first argument, call the correct metaclass.
> - This calls M_B.__new__, which again calls type.__new__,
> but this time with M_B as the first argument, which
> is correct.
This is a very good explanation and it should go somewhere in the
I remember I spent a significant amount of time and effort to reach the
a while ago, and now I have already started to forget eveything a again
Anyway, I will bookmark this post for future reference ;)
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