Just van Rossum
It is based on python and has a very good svn integration.
We started using it recently and so far it's working really well. I love the svn (and wiki!) integration. However, I have no idea how well it scales to a project the size of Python.
Having extensively used both Trac and Bugzilla, let me say that the ticket tracker in Trac is a child-play version of Bugzilla. It might be enough for Python, though, if SF was enough till now. I thought that a large project like Python required something more advanced. Anyway, I'll shut up as I see there is a committee for this decision. The integration between tickets/svn/wiki in Trac is cute though, even if, after a while, you'd really want that mailman parsed that syntax as well (and maybe your MUA too :) -- Giovanni Bajo