We were having a problem with serving .py files as attachments this morning. It turns out the problem was in the primary rewrite rules so I've made this rule:
RewriteRule ^([^.]+)\.[^/]+/+(\d\d\d\d/\d\d\.\d\d/\d\d\d\d+/+.*) http://semantic.blogmatrix.com/users/$1/podcasts/$2
The first in it's group, that is, we'll attempt to serve attachments (recognized by all the \ds) before we look for .py files (in which URIs are normally passed straight through for mod_python handling by the secondary Apache).