[Python-Dev] PEP487: Simpler customization of class creation

Nick Coghlan ncoghlan at gmail.com
Tue Jul 19 10:34:07 EDT 2016

On 19 July 2016 at 16:41, Neil Girdhar <mistersheik at gmail.com> wrote:
> Yes, I see what you're saying.   However, I don't understand why
> __init_subclass__ (defined on some class C) cannot be used to implement the
> checks required by @abstractmethod instead of doing it in ABCMeta.  This
> would prevent metaclass conflicts since you could use @abstractmethod with
> any metaclass or no metaclass at all provided you inherit from C.

ABCMeta also changes how __isinstance__ and __issubclass__ work and
adds additional methods (like register()), so enabling the use of
@abstractmethod without otherwise making the type an ABC would be very
confusing behaviour that we wouldn't enable by default.

But yes, this change does make it possible to write a mixin class that
implements the "@abstractmethod instances must all be overridden to
allow instances to to be created" logic from ABCMeta without otherwise
turning the class into an ABC instance.


Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

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