[Python-ideas] OrderedCounter and OrderedDefaultDict

[Andrew Barnert]

On Oct 21, 2015, at 11:25, Jonathan Slenders <jonathan at slenders.be> wrote:
> 
> Just want to say that I'm happy to see that lately the disadvantages of inheritance (which are already known for a very long time) are getting more attention.
> It's not bad by definition, but there's so much truth in Sandy her talk and I think for many Python projects, we went way too far into "abusing" inheritance.
> Actually, it's a bit unfortunate that we made inheritance so user friendly and powerful in Python that for many people it became the logical way to extend or reuse some code.

One of the most important things people have learned about OO over the past two decades is that subtyping, implementation extension, and implementation mixins, and interface-extending mixins (think collections.abc.Sequence adding count for you) are all different things. Compared to the other languages in existence at the time of Python 1.x or even the 2.2/2.3 changeover, it's hard to fault Python. The fact that it can easily be used to write bad code is a little unfortunate, but the fact that it can also easily be used to write good code, when other languages either don't allow some things to be expressed, force them to be expressed in clumsy or limited ways, or force you to misuse inappropriate features instead more than makes up for it. In particular, any language that has fixed structure layouts and vtables makes is much more unfriendly to both kinds of mixins, and makes interface subtyping clumsy; Python has no such problems. Yeah, maybe we could design something better in 2015, but based on the knowledge people had at the time?