[Spivak]

Single use? No way that's what multiple inheritance and mixins are for. Inheritance being only for code reuse is explicitly about not creating a taxonomy. No more is-a just, "I need this code here." Hey this thing behaves like a mapping inherit from the MutipleMapping and get all the usual mapping methods for free. Hey this model needs created/updated_at, inherit from ChangeTracking and get those fields and helper methods for free.

Has-a doesn't make sense for code like the literal text reuse. It makes sense for composition and encapsulation.

Edit: I'm now realizing that Python has one of the only sane multiple inheritance implementations. It's no wonder the rest of y'all hate it.