On Sat, 4 Jun 2016 09:52 pm, Gregory Ewing wrote: > Ian Kelly wrote: >> >> It can't belong to a subclass; the MRI guarantees that. But it's not >> necessarily a superclass either. > > Er, yes, what I really meant to say was that it could > be a class that got introduced into the MRO as a result > of someone else subclassing your class. > > So when you make a super call, you really have *no idea* > what it's going to call.
That's the nature of inheritance in a MI world. If you try to specify a particular superclass manually, you're in the position of the archetypal drunk looking for his lost car keys under a street light "because the light is better here". Sure, you always know which class you're calling, but sometimes its the wrong class! That's the mind-twisting part of MI. Just because your class inherits from K, doesn't mean that you should be calling K's methods. Until you (generic you) come to terms with that, you're going to struggle with MI regardless of what you do. It might help to read Michele Simionato's articles about super, multiple inheritance and related topics. Michele has been working with issues related to MI for many years and has a lot to say about them. Things to know about super: Part 1 http://www.artima.com/weblogs/viewpost.jsp?thread=236275 Part 2 http://www.artima.com/weblogs/viewpost.jsp?thread=236278 Part 3 http://www.artima.com/weblogs/viewpost.jsp?thread=237121 The wonders of super: http://www.artima.com/weblogs/viewpost.jsp?thread=281127 Mixins considered harmful: Part 1 http://www.artima.com/weblogs/viewpost.jsp?thread=246341 Part 2 http://www.artima.com/weblogs/viewpost.jsp?thread=246483 Part 3 http://www.artima.com/weblogs/viewpost.jsp?thread=254367 Part 4 http://www.artima.com/weblogs/viewpost.jsp?thread=254507 Traits as an alternative to MI and mixins: http://www.artima.com/weblogs/viewpost.jsp?thread=246488 Generic functions as an alternative to mixins: http://www.artima.com/weblogs/viewpost.jsp?thread=237764 The Method Resolution Order: https://www.python.org/download/releases/2.3/mro/ Michele wrote: "... the problem is multiple inheritance itself. Inheritance makes your code heavily coupled and difficult to follow (spaghetti inheritance). I have not found a real life problem yet that I could not solve with single inheritance + composition/delegation in a better and more maintainable way than using multiple inheritance." and I think that is the most valuable lesson here. MI itself is, if not an anti-pattern, at least a dangerous one. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
