What is a mixin, and why are they useful?

Question

In \"Programming Python\", Mark Lutz mentions \"mixins\". I\'m from a C/C++/C# background and I have not heard the term before. What is a mixin?

Reading between the

Answer 1

Perhaps a couple of examples will help.

If you're building a class and you want it to act like a dictionary, you can define all the various __ __ methods necessary. But that's a bit of a pain. As an alternative, you can just define a few, and inherit (in addition to any other inheritance) from UserDict.DictMixin (moved to collections.DictMixin in py3k). This will have the effect of automatically defining all the rest of the dictionary api.

A second example: the GUI toolkit wxPython allows you to make list controls with multiple columns (like, say, the file display in Windows Explorer). By default, these lists are fairly basic. You can add additional functionality, such as the ability to sort the list by a particular column by clicking on the column header, by inheriting from ListCtrl and adding appropriate mixins.