There is a Python article in the April 2001 issue of the Linux Journal,
"Using Mix-ins with Python". It covers the general topic of mix-in
programming with some comments on various languages, and then dives into
Python specifics including examples.
I used these concepts when creating the MiddleKit component of Webware
(http://webware.sourceforge.net/), which includes a mix-in function in
Get web dev at http://webware.sourceforge.net/