“Traits/roles instead of ABCs”, by Collin Winter.
With ABCs refererring to Abstract Base Classes (pep 3119).
Winter’s proposal is similar to my recent post, which is that this sort of “capability inference” should be dynamic, and not bound to the rigid nature of the class hierarchy. In my post on this subject, I showed a number of different implementations of a single interface (specification, role, whatever) - only one implementation followed the basic class-instance scenario. All others provided the exact same outward appearance, while internally they were implemented as module-level functions, class or static methods, or a dynamically composed single-use object (a brainless instance was made and had methods dynamically attached).
Winter’s roles/traits system, which refers to roles in Perl 6 and traits in Squeak, is along the same lines. I hope to hell it gains traction.