Not a prep course, but for example Redis has a very good source code overview here https://github.com/antirez/redis#redis-internals

More remarkable is the fact that antirez updated the documentation in response to a post in Reddit. https://www.reddit.com/r/redis/comments/3re0aw/any_pointers_... Thank you antirez! :-)

Shameless plug here but I have put together a free ebook detailing the inner workings of the python virtual machine @ https://leanpub.com/insidethepythonvirtualmachine

I agree - this basically gives you enough information to bootstrap your own learning about the CPython internals. I feel like all companies/projects should have a similar intro which gives new-joiners enough information that they can figure out most things themselves without too much pain, and without spoon-feeding too much.