Core Python Programming (2nd Edition)

7.11. Related Modules

The sets module became available in 2.3 and may be useful if you wish to subclass the Set or ImmutableSet classes. Although set types were integrated into Python 2.4, there are currently no plans to deprecate the module.

Some general online references for sets which you may find useful include:

http://en.wikipedia.org/wiki/Set

http://www.geocities.com/basicmathsets/set.html

http://www.math.uah.edu/stat/foundations/Sets.xhtml