Gentoo Python Guide

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.

Gentoo Python Guide 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.

No more PYTHON_TARGETS in single-r1

Since its inception in 2012, python-single-r1 has been haunting users with two sets of USE flags: PYTHON_TARGETS and PYTHON_SINGLE_TARGET. While this initially seemed a necessary part of the grand design, today I know we could have done better. Today this chymera is disappearing for real, and python-single-r1 are going to use PYTHON_SINGLE_TARGET flags only.

I would like to take this opportunity to explain why the eclass has been designed this way in the first place, and what has been done to change that.
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A better ebuild workflow with pure git and pkgcheck

Many developers today continue using repoman commit as their primary way of committing to Gentoo. While this tool was quite helpful, if not indispensable in times of CVS, today it’s a burden. The workflow using a single serial tool to check your packages and commit to them is not very efficient. Not only it wastes your time and slows you down — it discourages you from splitting your changes into more atomic commits.

Upon hearing the pkgcheck advocacy, many developers ask whether it can commit for you. It won’t do that, that’s not its purpose. Not only it’s waste of time to implement that — it would actually make it a worse tool. With its parallel engine pkgcheck really shines when dealing with multiple packages — forcing it to work on one package is a waste of its potential.

Rather than trying to proliferate your bad old habits, you should learn how to use git and pkgcheck efficiently. This post aims to give you a few advices.

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new* helpers can read from stdin

Did you know that new* helpers can read from stdin? Well, now you know! So instead of writing to a temporary file you can install your inline text straight to the destination:

src_install() {
  # old code
  cat <<-EOF >"${T}"/mywrapper || die
    #!/bin/sh
    exec do-something --with-some-argument
  EOF
  dobin "${T}"/mywrapper

  # replacement
  newbin - mywrapper <<-EOF
    #!/bin/sh
    exec do-something --with-some-argument
  EOF
}