How to create an ontology in python?

You can use rdflib for storing triples. You then have to make your own decisions about the kind of ontology you want to build. Look at the OWL format for that.

I toyed with python and ontologies during my PhD, so perhaps a quick scan through my thesis can give you some ideas. For instance a short OWL summary or a UML model of a plone ontology tool.

http://seth-scripting.sourceforge.net/

RDFLIB is a mature implementation of a triple store, with plenty of documentation.

However, this library worked for me only for smaller projects. For example there is a nice RDF/XML catalog of the Gutenberg Project Library, which i wasn't able to hack around with (on my dual-core, 2GBRAM machine), because it's simply too large (~ 100M) - even Java/Protege had a tendency to stall on this filesizes. It's a pity.

Alternative: http://seth-scripting.sourceforge.net/