When I took a look at the python.org Py3k poll, I saw that Mercurial was on the top list of things people wanted ported (though far behind the likes of Django). Now, I don’t know why others want to tie into Mercurial from code, but if a little performance overhead from using the CLI isn’t critical – such as when writing hooks, or just integrating version control in some tool or another, you might want to consider hgapi.
hgapi uses only the command line interface, and was created to be able to release autohook under a more permissive license than the GPL – and it’s tested against both Python 2.7 and Python 3.2. It now supports most (for a given computation of ’most’) operations in Mercurial, and as a bonus there are no open feature requests – so if there is something you miss, this is the time to request it!
Also, don’t forget to register for PyCon, early bird rates until 25/1!