[issue11610] Improved support for abstract base classes with descriptors

[Darren Dale]

Darren Dale <dsdale24 at gmail.com> added the comment:

On Sat, Jun 11, 2011 at 8:55 AM, Nick Coghlan <report at bugs.python.org> wrote:
>
> Nick Coghlan <ncoghlan at gmail.com> added the comment:
>
> inspect.getattr_static has the necessary logic to search for descriptors without invoking them.

Unfortunately, we can't import inspect, even inside ABCMeta.__new__.

> However, it may be better to revert to the idea of pushing this functionality back onto the individual descriptors and have the problematic descriptors like property and staticmethod simply implement __isabstractmethod__ as a property.
>
> property:
>  @property
>  def __isabstractmethod__(self):
>    return (self.fget.__isabstractmethod__ or
>            self.fset.__isabstractmethod__ or
>            self.fdel.__isabstractmethod__)
>
> staticmethod/classmethod:
>
>  @property
>  def __isabstractmethod__(self):
>    return self.__func__.__isabstractmethod__

That's a good idea.

> With this approach, the "one true way" to handle abstract descriptors would be to do:
>
>  #instance method
>  @abstractmethod
>  def f(self):
>    ...
>
>  @property
>  @abstractmethod
>  def f(self):
>    ...
>
>  @classmethod
>  @abstractmethod
>  def f(self):
>    ...
>
>  @staticmethod
>  @abstractmethod
>  def f(self):
>    ...
>
> This wouldn't allow for the prettier error messages, but it's much cleaner than having ABCMeta trawling through class attribute dir() lists.

Those classes could conceivably do:

@property
def __abstractmethods__(self):
    return ("...", ...)

It would not be required, but if ABCMeta found it, it could use it.
Just a thought.

Darren

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue11610>
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