I now have a working avro service (the mail service from pat hunt's excellent avro tutorial).
At this stage my Python implementation provides a superset of functionality of the existing Python implementation. Given that I have five code files, more tests, and a few thousand lines of code to review, and the existing Python maintainer has not been involved in the project for some time, I'd like to suggest replacing the existing implementation with this implementation and I can contribute the refactorings as part of the Avro project rather than continuing to work on github.
Lots of planned refactorings and extra tests! I also have a large file of implementation notes with a lot of questions that should help clarify things for future implementors (http://github.com/hammer/avro/blob/trunk/src/py/avro/IMPLEMENTATION_NOTES.md).
Super excited to work on the cross-project test schemas soon.