Tree and Graph structures in Python.

[bearophileHUGS at lycos.com]

http://www.osl.iu.edu/~dgregor/bgl-python/
http://sourceforge.net/projects/pygraphlib/
http://sourceforge.net/projects/pynetwork/
https://networkx.lanl.gov/
http://starship.python.net/crew/aaron_watters/kjbuckets/
http://www.python.org/doc/essays/graphs.html
http://yapgvb.sourceforge.net/
http://dkbza.org/pydot.html
http://www.geocities.com/foetsch/mfgraph/index.htm

(Some of them are just explanations, or interfaces with a well known
graph plotting package).
With Google you can probably find 2-4 other libraries...
I think there are so many of them because some people need them, but
there isn't a standard one yet in the built-in library.

Bye,
bearophile