Sure! It's quite simple: works like a charm. Completely transparent. You `import` with Python-like syntax, and you get a Ruby object that transparently forwards any message (i.e. method calls) to the corresponding Python object on the underlying Python interpreter.
This means that Ruby does not need to know _anything_ about the Python object: whatever you call on the Ruby object is just forwarded to the Python one, and whatever result is passed back to Ruby.
About the overhead, I sincerely do not know; I expected to have some so my code does part of the image pre-processing directly in Python (`narray`) in order to pass a smaller object to Ruby, but besides that I could perceive none -- grain of salt advised, as that was possibly hidden from me because my computation in Ruby was orders of magnitude more complex/time consuming than what was going on on the Python interpreter.
Definitely ping Murata-san either on GitHub https://github.com/mrkn/pycall.rb/ or Twitter `@mrkn`, I will send him a link to this thread so he can contribute if he feels like it. Personally, I am a fan of his work and elegant approach, I owe him for enabling me to keep working in Ruby while everybody publishes code in Python :)
Sounds great - I also prefer Ruby very strongly, and have tended to avoid Python code because I didn't expect to have an easy way of wrapping it, but will definitively have to play with Pycall.