[issue5867] No way to create an abstract classmethod

[Daniel Urban]

Daniel Urban <urban.dani+py at gmail.com> added the comment:

@abstractmethod
@classmethod
def ...
doesn't work because classmethod objects doesn't have a __dict__, so setting arbitrary attributes don't work, and abstractmethod tries to set the __isabstractmethod__ atribute to True.


The other order:
@classmethod
@abstractmethod
def ...
doesn't work, because the abstractmethod decorator sets the function's __isabstractmethod__ attribute to True, but when ABCMeta.__new__ checks the object in the namespace of the class, it won't find it, because the classmethod object won't have an __isabstractmethod__ attribute.

The situation is the same with staticmethod.

One possible solution would be adding a descriptor to classmethod (and staticmethod), with the name "__isabstractmethod__", which on __get__ would check its underlying callable for this attribute, and on __set__ would set this attribute on that callable. I think this way both order should work.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue5867>
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