Using a Ruby gem from a Django application
I suggest you either:

Expose a ruby service using REST or XML-RPC.

or 

Shell out to a ruby script from Django.

To transfer data between Python and Ruby I suggest you use JSON, XML or plain text (depending on what kind of data you need to transfer).
I would recommend to use option 2 (start a ruby script from the Python process), as this introduces fewer moving parts to the solution.
Lets say I have a few Ruby gems that I'd like to use from my Python (Django) application. I know this isn't the most straightforward question but let's assume that rewriting the Ruby gem in Python is a lot of work, how can I use it?
Should I create an XML-RPC wrapper around it using Rails and call it? Is there something like a ruby implementation in Python within which I could run my gem code?
Are there other methods that I may have missed? I've never tacked anything like this before I was a bit lost in this area.
Thanks