[Tutor] What is a mixin class?

[Kent Johnson]

(resending to the whole list)

Don Taylor wrote:
> I have a vague idea what a mixin class is, I would like to get a better 
> handle on it.
> 
> It is a term that is used quite often in Python circles, but I can't 
> find a definition.
> 
> I guess that because of multiple inheritance Python does not need a 
> formal way of specifying mixin classes so I presume that there is some 
> conventional interpretation/coding that is followed for mixin classes.
> 
> So, what constitutes a mixin class and what are the conventional ways to 
> denote them in code?
> 
> Don.
> 
> I notice that Ruby has single inheritance plus mixin classes so maybe 
> somebody who knows Ruby could throw some light on in what way a mixin is 
> different from normal superclass.

A mixin is a class that is not intended to stand on its own, rather it
adds some behaviour to the class that it is mixed in to. Some discussion
here:
http://en.wikipedia.org/wiki/Mixin
http://c2.com/cgi/wiki?Mixin

This page
http://c2.com/cgi/wiki?MixinsForPython
points to SocketServer.ForkingMixin and SocketServer.ThreadingMixin as
examples from the Python standard library.

HTH,
Kent