The bullet item links will take you directly to my specific contributions.
I think my contributions to Pyramid, from the Pylons project, at the last two PyCons are the best to demonstrate my Python skills. I added Python 2.5-3.3 compatibility to the packages providing an email API to Pyramid apps, repoze.sendmail and pyramid_mailer.
It's not the most exciting stuff in the world, but it demonstrates my dedication to best practices, Test Driven Development, ability to jump into an existing code base, and eagerness to find a place to contribute based more on it's value to the community than to how exciting it may appear.
You may also want to look at IISWSGI, a WSGI to Microsoft's IIS FCGI bridge and set of tools for deploying apps on IIS using Microsoft's Web Platform Installer. It's not pretty or complete so I don't cite it as an example of best Python practices. In particular there are no tests and probably some serious bugs that would come out if used in production. Rather I cite it as an example of my ability to tackle a problem no one else would, to build tools that integrate with very opaque systems (such as IIS's FCGI implementation, the internals of the Web Platform Installer, and Microsoft in general) by working hard to find ways to get insight into those opaque systems, and to deliver a working prototype of the course of one sprint. I tackled it because Plone, the open-source enterprise Python CMS and a project I've had a long involvement with and made considerable contributions to, has always had problems with it's Windows deployment story. No one wanted to tackle it, including myself,but it was needed so I developed the start of a path forward. Unfortunately, though everyone likes to complain about the problems in our Windows support, there's never enough interest for community ownership, so IISWSGI has languished since then. It may still serve as a good example for your consideration:
Aside from that I'll point in general to my contributions to the Plone project. I've been a member of the Framework Team, the team responsible for reviewing and evaluating proposals of what will go into the next major release, and am currently a member of the Testing Team, the team responsible for developing and maintaining the testing infrastructure for the project including everything from testing fixtures, testing tools for use by developers writing tests,acceptance testing infrastructure, and continuous integration. I've attended numerous sprints and love the team and community spirit that comes with working on such a vibrant project.