[Python-ideas] abc.optionalabstractmethod

[Masklinn]

On 2012-08-02, at 17:26 , Eric Snow wrote:

> Sometimes you want to specific an optional method in an abstract base
> class.  Currently we don't have a consistent way of doing so, instead
> having to mix in the old way of defining "abstract" methods:
> 
> class MyABC(metaclass=ABCMeta):
>    ...
> 
>    def do_something_optional(self):
>        """An optional method for doing something."""
>        raise NotImplementedError
> 
> This came up in issue 15502[1], where we are splitting
> importlib.abc.Finder into MetaPathFinder and PathEntryFinder.  These
> have a method, invalidate_caches(), which is optional.  It would be
> nice to have a new decorator akin to abstractmethod that would allow
> defining an optional interface in a consistent way.  Something like
> optionalabstractmethod (or some better name).  Then the above example
> would be like this:
> 
> class MyABC(metaclass=ABCMeta):
>    ...
> 
>    @optionalabstractmethod
>    def do_something_optional(self):
>        """An optional method for doing something."""
> 
> Thoughts?

Wouldn't it be better to have a generic @optional applying to all @abstract*? e.g.

class MyABC*metaclass=ABCMeta):
    @optional
    @abstractmethod
    def do_something_optional(self):
        """ an optional method for doing something """

(yeah I know all of them apart from @abstractmethod are deprecated, still it
feels ugly and unreadable to have @optionalabstractmethod next to @abstractmethod)