Gentoo provides one of the best frameworks for providing Python support in packages among operating systems. This includes support for running multiple versions of Python (while most other distributions avoid going beyond simultaneous support for Python 2 and one version of Python 3), alternative implementations of Python, reliable tests, deep QA checks. While we aim to keep things simple, this is not always possible.
At the same time, the available documentation is limited and not always up-to-date. Both the built-in eclass documentation and Python project wiki page provide bits of documentation but they are mostly in reference form and not very suitable for beginners nor people who do not actively follow the developments within the ecosystem. This results in suboptimal ebuilds, improper dependencies, missing tests.
This document aims to fill the gap by providing a good, complete, by-topic (rather than reference-style) documentation for the ecosystem in Gentoo and the relevant eclasses. Combined with examples, it should help you write good ebuilds and solve common problems as simply as possible.
Gentoo Python Guide sources are available on GitHub. Suggestions and improvements are welcome.