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Super considered super!

In an entertaining and very accessible talk by Raymond Hettinger, he describes the design principles of super() and how it can be used to implement multiple cooperative inheritance (See the blog post for all the neat details!).

Additionally, you can also have a look at a great StackOverflow answer and several posts written by Guido himself on Method Resolution Order (MRO) for rationale behind the design and other details.

In brief, the core ideas of the talk were:

  1. super() complements the idea of reusing code and DRY principles using inheritance.

  2. multiple inheritance (especially Diamond) pattern used to be hard but not now, iff you understand how super() works.

  3. Python’s super() is different than the super in other languages. In Python, it means next-in-line (the line here being Method Resolution Order - MRO) determined by stable, deterministic algorithm) and thus may not necessarily refer the parent.

  4. super() can be used for dependency injection.

A couple of notes, however, when using super():

  • In Python 2, super() accepted arguments - the current item in MRO and the MRO tree of the original object. In Py3k, it is implicitly calculated.
  • Use kwargs to deal issues with position arguments.
  • Put a stopper class at the end of the chain call.
  • In case a class in non-cooperative, just subclass it to create another that uses super().

I hope that it will help me better understand large projects and code organization. Not to mention, use it my own projects as well.