FWIW, I've come to regard this (cooperative multiple inheritance) as a failed experiment. It's just been too confusing, and hasn't seen adoption.
Instead, I've come to prefer a style I took from Julia: every class is either (a) abstract, or (b) concrete and final.
Abstract classes exist to declare interfaces.
__init__ methods only exist on concrete classes. After that it should be thought of as unsubclassable, and concerns about inheritance and diamond dependencies etc just don't exist.
(If you do need to extend some functionality: prefer composition over inheritance.)
Instead, I've come to prefer a style I took from Julia: every class is either (a) abstract, or (b) concrete and final.
Abstract classes exist to declare interfaces.
__init__ methods only exist on concrete classes. After that it should be thought of as unsubclassable, and concerns about inheritance and diamond dependencies etc just don't exist.
(If you do need to extend some functionality: prefer composition over inheritance.)