Do we need to define importlib.abc.PathEntryFinder.find_spec() #103999

importlib.abc.PathEntryFinder has this comment: "We don't define find_spec() here since that would break hasattr checks we do to support backward compatibility." Do we need to define find_spec() in this ABC?

importlib.abc.MetaPathFinder has the same comment. Just in case someone looks at this issue later and is confused: PathEntryFinder doesn't have the comment anymore, it was removed in #98059, but it was there before that.

One problem: importlib.metadata.DistributionFinder inherits from MetaPathFinder. That's another abstract class, which in turn is a base class for the concrete importlib.metadata.MetadataPathFinder. MetadataPathFinder does not implement find_spec, and either it or DistributionFinder would need to if find_spec is added to MetaPathFinder as an abstract method. The documented failure state for find_spec is just to return None, so maybe that's fine. Or find_spec can be added to MetaPathFinder with a default implementation that just returns None.

All the documentation says these ABCs have these as abstract methods; it'd be good to have that be true. I think probably the right thing for MetaPathFinder is to have the abstract method, and then an implementation on DistributionFinder that just returns None.

One final wrinkle: All the implementations of MetaPathFinder in the standard library have find_spec as a classmethod. We don't document it as a classmethod on MetaPathFinder, and looking at the first page of github search results, I didn't see any third-party users who implemented find_spec as a classmethod. Should it be a classmethod on MetaPathFinder?