I looked at the example blog and I think the problem is it doesn't include "autoconfig" information in an RSD file. This would help MarsEdit to automatically detect that it has WordPress-style features.
One trick you can try is to point MarsEdit at another WordPress blog temporarily, to get it configured right, and then switch the settings back to your micolog API Endpoint:
1. Open the blog settings for your blog in MarsEdit.
2. Make a note of the API Endpoint URL (you'll paste it back in a minute).
3. Change the home page URL temporarily to:
http://sweatertest.wordpress.com/
4. Click the auto-detect settings button again.
5. Now change the API Endpoint URL back to your blog, and change the home page URL back to your blog. Don't click Auto-Detect again.
This is a way of tricking MarsEdit into thinking your blog has all the modern WordPress features (like Tags) even if it isn't correctly autodetecting.
I don't know of any other Python-based blog systems off the top of my head. Maybe somebody else will chime in with information for you.
Daniel