I have used the guide when at college and it was an extremely good read at the time. Learnt so much. I should probably buy a printed copy.

Being that said, at the moment I'm trying to implement a simple non-blocking TLS server in Python with a custom protocol (no external deps, only built-ins) and couldn't find a single guide online that treats the topic. Having read the Python documentation it appears that there are a lot of nuances and pitfalls to correctly implement it. This was my impression after reading the docs, though I could be wrong.

I haven't checked if current Beej's guide covers the topic, in case it doesn't, did anyone embarked in doing this with success?

The Python docs on the topic: https://docs.python.org/3/library/ssl.html#ssl-nonblocking