We have __slots__ with other ABC's, seehttp://bugs.python.org/issue11333 andhttp://bugs.python.org/issue21421.There are no downsides to having empty slots on a non-instantiable class, but it does give the option of denying __dict__ creation for subclassers. The possibility of breaking is for someone using __slots__ but relying on __dict__ creation in a subclass - they will have to explicitly add "__dict__" to __slots__. Since we have added __slots__ to other ABC's, I will provide a PR soon on this. Diff should look like this (inLib/abc.py):class ABC(metaclass=ABCMeta):    """Helper class that provides a standard way to create an ABC using    inheritance.    """- pass+ __slots__ = ()(I also want to add a test for this, and ensure other ABC's also have this if they don't.)

This seems reasonable.

New changesetff48739ed0a3f366c4d56d3c86a37cbdeec600de by Serhiy Storchaka (Aaron Hall, MBA) in branch 'master':bpo-30463: Add an empty __slots__ to abc.ABC.https://github.com/python/cpython/commit/ff48739ed0a3f366c4d56d3c86a37cbdeec600de

I will note that this means with:class BaseClass(ABC):    passclass MyDerivedClass(BaseClass):    def __init__(self, thing):        self.thing = thingthing = MyDerivedClass()thing now has both __slots__ and, evidently, a dict. That's a bit weird and confusing.