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<section id="maintenance-of-python-implementations">
<h1>Maintenance of Python implementations<a class="headerlink" href="#maintenance-of-python-implementations" title="Link to this heading">¶</a></h1>
<section id="notes-specific-to-python-interpreters">
<h2>Notes specific to Python interpreters<a class="headerlink" href="#notes-specific-to-python-interpreters" title="Link to this heading">¶</a></h2>
<section id="cpython-patchsets">
<h3>CPython patchsets<a class="headerlink" href="#cpython-patchsets" title="Link to this heading">¶</a></h3>
<p>Gentoo is maintaining patchsets for all CPython versions. These include
some non-upstreamable Gentoo patches and upstream backports. While it
is considered acceptable to add a new patch (e.g. a security bug fix)
to <code class="docutils literal notranslate"><span class="pre">files/</span></code> directory, it should be eventually moved into
the respective patchset.</p>
<p>When adding a new version, it is fine to use an old patchset if it
applies cleanly. If it does not, you should regenerate the patchset
for new version.</p>
<p>The origin for Gentoo patches are the <code class="docutils literal notranslate"><span class="pre">gentoo-*</span></code> tags the <a class="reference external" href="https://gitweb.gentoo.org/fork/cpython.git/">Gentoo fork
of CPython repository</a>. The recommended workflow is to clone
the upstream repository, then add Gentoo fork as a remote, e.g.:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">git</span> <span class="n">clone</span> <span class="n">https</span><span class="p">:</span><span class="o">//</span><span class="n">github</span><span class="o">.</span><span class="n">com</span><span class="o">/</span><span class="n">python</span><span class="o">/</span><span class="n">cpython</span>
<span class="n">cd</span> <span class="n">cpython</span>
<span class="n">git</span> <span class="n">remote</span> <span class="n">add</span> <span class="n">gentoo</span> <span class="n">git</span><span class="nd">@git</span><span class="o">.</span><span class="n">gentoo</span><span class="o">.</span><span class="n">org</span><span class="p">:</span><span class="n">fork</span><span class="o">/</span><span class="n">cpython</span><span class="o">.</span><span class="n">git</span>
<span class="n">git</span> <span class="n">fetch</span> <span class="o">--</span><span class="n">tags</span> <span class="n">gentoo</span>
</pre></div>
</div>
<p>In order to rebase the patchset, check out the tag corresponding
to the previous patchset version and rebase it against the upstream
release tag:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">git</span> <span class="n">checkout</span> <span class="n">gentoo</span><span class="o">-</span><span class="mf">3.7.4</span>
<span class="n">git</span> <span class="n">rebase</span> <span class="n">v3</span><span class="mf">.7.6</span>
</pre></div>
</div>
<p>You may also add additional changes via <code class="docutils literal notranslate"><span class="pre">git</span> <span class="pre">cherry-pick</span></code>. Once
the new patches are ready, create the tarball and upload it, then
create the tag and push it:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">mkdir</span> <span class="n">python</span><span class="o">-</span><span class="n">gentoo</span><span class="o">-</span><span class="n">patches</span><span class="o">-</span><span class="mf">3.7.6</span>
<span class="n">cd</span> <span class="n">python</span><span class="o">-</span><span class="n">gentoo</span><span class="o">-</span><span class="n">patches</span><span class="o">-</span><span class="mf">3.7.6</span>
<span class="n">git</span> <span class="nb">format</span><span class="o">-</span><span class="n">patch</span> <span class="n">v3</span><span class="mf">.7.6</span>
<span class="n">cd</span> <span class="o">..</span>
<span class="n">tar</span> <span class="o">-</span><span class="n">cf</span> <span class="n">python</span><span class="o">-</span><span class="n">gentoo</span><span class="o">-</span><span class="n">patches</span><span class="o">-</span><span class="mf">3.7.6</span><span class="o">.</span><span class="n">tar</span> <span class="n">python</span><span class="o">-</span><span class="n">gentoo</span><span class="o">-</span><span class="n">patches</span><span class="o">-</span><span class="mf">3.7.6</span>
<span class="n">xz</span> <span class="o">-</span><span class="mi">9</span> <span class="n">python</span><span class="o">-</span><span class="n">gentoo</span><span class="o">-</span><span class="n">patches</span><span class="o">-</span><span class="mf">3.7.6</span><span class="o">.</span><span class="n">tar</span>
<span class="n">scp</span> <span class="n">python</span><span class="o">-</span><span class="n">gentoo</span><span class="o">-</span><span class="n">patches</span><span class="o">-</span><span class="mf">3.7.6</span><span class="o">.</span><span class="n">tar</span><span class="o">.</span><span class="n">xz</span> <span class="o">...</span>
<span class="n">git</span> <span class="n">tag</span> <span class="n">gentoo</span><span class="o">-</span><span class="mf">3.7.6</span>
<span class="n">git</span> <span class="n">push</span> <span class="o">--</span><span class="n">tags</span> <span class="n">gentoo</span>
</pre></div>
</div>
</section>
<section id="pypy">
<h3>PyPy<a class="headerlink" href="#pypy" title="Link to this heading">¶</a></h3>
<p>Due to high resource requirements and long build time, PyPy on Gentoo
is provided both in source and precompiled form. This creates a bit
unusual ebuild structure:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">dev-python/pypy-exe</span></code> provides the PyPy executable and generated
files built from source,</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">dev-python/pypy-exe-bin</span></code> does the same in precompiled binary form,</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">dev-python/pypy</span></code> combines the above with the common files. This
is the package that runs tests and satisfies the PyPy target.</p></li>
</ul>
<p>Matching <code class="docutils literal notranslate"><span class="pre">dev-python/pypy3*</span></code> exist for PyPy3.</p>
<p>When bumping PyPy, <code class="docutils literal notranslate"><span class="pre">pypy-exe</span></code> needs to be updated first. Then it
should be used to build a binary package and bump <code class="docutils literal notranslate"><span class="pre">pypy-exe-bin</span></code>.
Technically, <code class="docutils literal notranslate"><span class="pre">pypy</span></code> can be bumped after <code class="docutils literal notranslate"><span class="pre">pypy-exe</span></code> and used to test
it but it should not be pushed before <code class="docutils literal notranslate"><span class="pre">pypy-exe-bin</span></code> is ready, as it
would force all users to switch to source form implicitly.</p>
<p>The binary packages are built using <a class="reference external" href="https://www.docker.com/">Docker</a> nowadays, using
<a class="reference external" href="https://github.com/mgorny/binpkg-docker">binpkg-docker</a> scripts. To produce them, create a <code class="docutils literal notranslate"><span class="pre">local.diff</span></code>
containing changes related to PyPy bump and run <code class="docutils literal notranslate"><span class="pre">amd64-pypy</span></code>
(and/or <code class="docutils literal notranslate"><span class="pre">amd64-pypy3</span></code>) and <code class="docutils literal notranslate"><span class="pre">x86-pypy</span></code> (and/or <code class="docutils literal notranslate"><span class="pre">x86-pypy3</span></code>) make
targets:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">git</span> <span class="n">clone</span> <span class="n">https</span><span class="p">:</span><span class="o">//</span><span class="n">github</span><span class="o">.</span><span class="n">com</span><span class="o">/</span><span class="n">mgorny</span><span class="o">/</span><span class="n">binpkg</span><span class="o">-</span><span class="n">docker</span>
<span class="n">cd</span> <span class="n">binpkg</span><span class="o">-</span><span class="n">docker</span>
<span class="p">(</span><span class="n">cd</span> <span class="o">~/</span><span class="n">git</span><span class="o">/</span><span class="n">gentoo</span> <span class="o">&&</span> <span class="n">git</span> <span class="n">diff</span> <span class="n">origin</span><span class="p">)</span> <span class="o">></span> <span class="n">local</span><span class="o">.</span><span class="n">diff</span>
<span class="n">make</span> <span class="n">amd64</span><span class="o">-</span><span class="n">pypy</span> <span class="n">amd64</span><span class="o">-</span><span class="n">pypy3</span> <span class="n">x86</span><span class="o">-</span><span class="n">pypy</span> <span class="n">x86</span><span class="o">-</span><span class="n">pypy3</span>
</pre></div>
</div>
<p>The resulting binary packages will be placed in your home directory,
in <code class="docutils literal notranslate"><span class="pre">~/binpkg/${arch}/pypy</span></code>. Upload them and use them to bump
<code class="docutils literal notranslate"><span class="pre">pypy-exe-bin</span></code>.</p>
</section>
</section>
<section id="adding-a-new-python-implementation">
<h2>Adding a new Python implementation<a class="headerlink" href="#adding-a-new-python-implementation" title="Link to this heading">¶</a></h2>
<section id="eclass-and-profile-changes">
<h3>Eclass and profile changes<a class="headerlink" href="#eclass-and-profile-changes" title="Link to this heading">¶</a></h3>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The best time to perform these changes is prior to adding the first
beta of new Python version. This is because <code class="docutils literal notranslate"><span class="pre">dev-lang/python</span></code>
has a conditional dependency on <code class="docutils literal notranslate"><span class="pre">dev-lang/python-exec</span></code>
for non-alpha versions, so adding the target prior to committing it
ensures depgraph consistency.</p>
</div>
<p>When adding a new Python target, please remember to perform all
the following tasks:</p>
<ul class="simple">
<li><p>add the new target flags to <code class="docutils literal notranslate"><span class="pre">profiles/desc/python_targets.desc</span></code>
and <code class="docutils literal notranslate"><span class="pre">python_single_target.desc</span></code>.</p></li>
<li><p>force the new implementation on <code class="docutils literal notranslate"><span class="pre">dev-lang/python-exec</span></code>
via <code class="docutils literal notranslate"><span class="pre">profiles/base/package.use.force</span></code>.</p></li>
<li><p>mask the new target flags on stable profiles
via <code class="docutils literal notranslate"><span class="pre">profiles/base/use.stable.mask</span></code>.</p></li>
<li><p>update <code class="docutils literal notranslate"><span class="pre">python-utils-r1.eclass</span></code>:</p>
<ol class="arabic simple">
<li><p>add the implementation to <code class="docutils literal notranslate"><span class="pre">_PYTHON_ALL_IMPLS</span></code></p></li>
<li><p>update the patterns in <code class="docutils literal notranslate"><span class="pre">_python_verify_patterns</span></code></p></li>
<li><p>update the patterns in <code class="docutils literal notranslate"><span class="pre">_python_set_impls</span></code></p></li>
<li><p>update the patterns in <code class="docutils literal notranslate"><span class="pre">_python_impl_matches</span></code></p></li>
<li><p>add the appropriate dependency to the case for <code class="docutils literal notranslate"><span class="pre">PYTHON_PKG_DEP</span></code></p></li>
</ol>
</li>
<li><p>update the tested version range in <code class="docutils literal notranslate"><span class="pre">eclass/tests/python-utils-r1.sh</span></code></p></li>
<li><p>add the new implementation to the list
in <code class="docutils literal notranslate"><span class="pre">app-portage/gpyutils/files/implementations.txt</span></code>.</p></li>
<li><p>update the <a class="reference external" href="https://wiki.gentoo.org/wiki/Project:Python/Implementations">implementation tables</a> on Gentoo wiki</p></li>
</ul>
</section>
<section id="porting-initial-packages">
<h3>Porting initial packages<a class="headerlink" href="#porting-initial-packages" title="Link to this heading">¶</a></h3>
<p>The initial porting is quite hard due to a number of circular
dependencies. To ease the process, it is recommended to temporarily
limit testing of the packages that feature many additional test
dependencies. The packages needing this have implementation conditions
in place already. An example follows:</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="nv">PYTHON_TESTED</span><span class="o">=(</span><span class="w"> </span>python3_<span class="o">{</span><span class="m">8</span>..10<span class="o">}</span><span class="w"> </span>pypy3<span class="w"> </span><span class="o">)</span>
<span class="w"> </span><span class="nv">PYTHON_COMPAT</span><span class="o">=(</span><span class="w"> </span><span class="s2">"</span><span class="si">${</span><span class="nv">PYTHON_TESTED</span><span class="p">[@]</span><span class="si">}</span><span class="s2">"</span><span class="w"> </span>python3_11<span class="w"> </span><span class="o">)</span>
<span class="w"> </span><span class="nv">BDEPEND</span><span class="o">=</span><span class="s2">"</span>
<span class="s2"> test? (</span>
<span class="hll"><span class="s2"> </span><span class="k">$(</span>python_gen_cond_dep<span class="w"> </span><span class="s1">'</span>
</span><span class="s1"> dev-python/jaraco-envs[${PYTHON_USEDEP}]</span>
<span class="s1"> >=dev-python/jaraco-path-3.2.0[${PYTHON_USEDEP}]</span>
<span class="s1"> dev-python/mock[${PYTHON_USEDEP}]</span>
<span class="s1"> dev-python/pip[${PYTHON_USEDEP}]</span>
<span class="s1"> dev-python/sphinx[${PYTHON_USEDEP}]</span>
<span class="s1"> dev-python/pytest[${PYTHON_USEDEP}]</span>
<span class="s1"> dev-python/pytest-fixture-config[${PYTHON_USEDEP}]</span>
<span class="s1"> dev-python/pytest-virtualenv[${PYTHON_USEDEP}]</span>
<span class="s1"> dev-python/pytest-xdist[${PYTHON_USEDEP}]</span>
<span class="s1"> >=dev-python/virtualenv-20[${PYTHON_USEDEP}]</span>
<span class="s1"> dev-python/wheel[${PYTHON_USEDEP}]</span>
<span class="hll"><span class="s1"> '</span><span class="w"> </span><span class="s2">"</span><span class="si">${</span><span class="nv">PYTHON_TESTED</span><span class="p">[@]</span><span class="si">}</span><span class="s2">"</span><span class="k">)</span>
</span><span class="s2"> )</span>
<span class="s2"> "</span>
<span class="w"> </span>python_test<span class="o">()</span><span class="w"> </span><span class="o">{</span>
<span class="hll"><span class="w"> </span>has<span class="w"> </span><span class="s2">"</span><span class="si">${</span><span class="nv">EPYTHON</span><span class="si">}</span><span class="s2">"</span><span class="w"> </span><span class="s2">"</span><span class="si">${</span><span class="nv">PYTHON_TESTED</span><span class="p">[@]/_/.</span><span class="si">}</span><span class="s2">"</span><span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="k">continue</span>
</span>
<span class="w"> </span><span class="nv">HOME</span><span class="o">=</span><span class="s2">"</span><span class="si">${</span><span class="nv">PWD</span><span class="si">}</span><span class="s2">"</span><span class="w"> </span>epytest<span class="w"> </span>setuptools
<span class="w"> </span><span class="o">}</span>
</pre></div>
</div>
<p>It is important to remember to update the implementation range
and therefore enable testing once the test dependencies are ported.
Please do not remove the conditions entirely, as they will be useful
for the next porting round.</p>
<p>If only a non-significant subset of test dependencies is a problem,
it is better to make these dependencies conditional and run
the remainder of the test suite. If tests are not skipped automatically
due to missing dependencies, using <code class="docutils literal notranslate"><span class="pre">has_version</span></code> to skip them
conditionally is preferred over hardcoding version ranges, e.g.:</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="nv">BDEPEND</span><span class="o">=</span><span class="s2">"</span>
<span class="s2"> test? (</span>
<span class="hll"><span class="s2"> </span><span class="k">$(</span>python_gen_cond_dep<span class="w"> </span><span class="s1">'</span>
</span><span class="hll"><span class="s1"> dev-python/pydantic[${PYTHON_USEDEP}]</span>
</span><span class="hll"><span class="s1"> '</span><span class="w"> </span>pypy3<span class="w"> </span>python3_<span class="o">{</span><span class="m">8</span>..10<span class="o">}</span><span class="w"> </span><span class="c1"># TODO: python3_11</span>
</span><span class="hll"><span class="w"> </span><span class="k">)</span>
</span><span class="s2"> )</span>
<span class="s2"> "</span>
<span class="w"> </span>python_test<span class="o">()</span><span class="w"> </span><span class="o">{</span>
<span class="w"> </span><span class="nb">local</span><span class="w"> </span><span class="nv">EPYTEST_DESELECT</span><span class="o">=()</span>
<span class="hll"><span class="w"> </span><span class="k">if</span><span class="w"> </span>!<span class="w"> </span>has_version<span class="w"> </span><span class="s2">"dev-python/pydantic[</span><span class="si">${</span><span class="nv">PYTHON_USEDEP</span><span class="si">}</span><span class="s2">]"</span><span class="p">;</span><span class="w"> </span><span class="k">then</span>
</span><span class="w"> </span><span class="nv">EPYTEST_DESELECT</span><span class="o">+=(</span>
<span class="w"> </span>tests/test_comparison.py::test_close_to_now_<span class="o">{</span>false,true<span class="o">}</span>
<span class="w"> </span><span class="o">)</span>
<span class="w"> </span><span class="k">fi</span>
<span class="w"> </span>epytest
<span class="w"> </span><span class="o">}</span>
</pre></div>
</div>
<p>During the initial testing it is acceptable to be more lenient on test
failures, and deselect failing tests on the new implementation when
the package itself works correctly for its reverse dependencies.
For example, during Python 3.11 porting we have deselected a few failing
tests on <code class="docutils literal notranslate"><span class="pre">dev-python/attrs</span></code> to unblock porting <code class="docutils literal notranslate"><span class="pre">dev-python/pytest</span></code>.
Porting pytest in order to enable testing packages was far more
important than getting 100% passing tests on <code class="docutils literal notranslate"><span class="pre">dev-python/attrs</span></code>.</p>
<p>The modern recommendation for the porting process is to focus
on <code class="docutils literal notranslate"><span class="pre">dev-python/pytest</span></code> as the first goal. It is the most common test
dependency for Python packages, and porting it makes it possible to
start testing packages early. The initial ported package set should
include all dependencies of pytest, except for test dependencies
of the package with large test dependency graphs (<code class="docutils literal notranslate"><span class="pre">dev-python/pytest</span></code>
itself, <code class="docutils literal notranslate"><span class="pre">dev-python/setuptools</span></code>). This amounts to around 40 packages.</p>
<p>Note that emerging the initial set requires installing
<code class="docutils literal notranslate"><span class="pre">dev-python/pytest</span></code> with <code class="docutils literal notranslate"><span class="pre">USE=-test</span></code> first. Once it is installed,
the previously installed dependencies should be reinstalled with tests
enabled.</p>
<p>After pushing the initial batch, the next recommended goal
is <code class="docutils literal notranslate"><span class="pre">dev-python/urllib3</span></code>. It should be followed by focusing
on reenabling tests in the packages where they were skipped.</p>
</section>
</section>
<section id="removing-a-python-implementation">
<h2>Removing a Python implementation<a class="headerlink" href="#removing-a-python-implementation" title="Link to this heading">¶</a></h2>
<section id="preparation">
<h3>Preparation<a class="headerlink" href="#preparation" title="Link to this heading">¶</a></h3>
<p>The obsolescence of the implementation needs to be announced on mailing
lists, along with request to proceed with porting packages to a newer
implementation. The package lists found on <a class="reference external" href="https://qa-reports.gentoo.org/">QA reports</a> can be used
to track the porting progress.</p>
<p>As the time for removal approaches, the packages showing no signs
of porting effort (except for backports, i.e. packages dedicated
to the old implementation and used only conditionally to it) need to
be masked for removal.</p>
</section>
<section id="id1">
<h3>Eclass and profile changes<a class="headerlink" href="#id1" title="Link to this heading">¶</a></h3>
<p>Rather than being removed entirely, old targets are implicitly disabled
via the eclass. This ensures that old entries in <code class="docutils literal notranslate"><span class="pre">PYTHON_COMPAT</span></code>
do not trigger errors.</p>
<p>When disabling an old target, please remember to:</p>
<ul class="simple">
<li><p>remove the <code class="docutils literal notranslate"><span class="pre">dev-lang/python-exec</span></code> dependency from the interpreter
ebuilds (with a revision bump)</p></li>
<li><p>mask and remove the remaining backport packages immediately (they
would fail to source once the only listed implementation is disabled
but the mask should remain to hint users at the removal)</p></li>
<li><p>update the tested version range in <code class="docutils literal notranslate"><span class="pre">eclass/tests/python-utils-r1.sh</span></code></p></li>
<li><p>update <code class="docutils literal notranslate"><span class="pre">python-utils-r1.eclass</span></code>:</p>
<ol class="arabic simple">
<li><p>move the implementation from <code class="docutils literal notranslate"><span class="pre">_PYTHON_ALL_IMPLS</span></code>
to <code class="docutils literal notranslate"><span class="pre">_PYTHON_HISTORICAL_IMPLS</span></code></p></li>
<li><p>update the patterns in <code class="docutils literal notranslate"><span class="pre">_python_set_impls</span></code></p></li>
<li><p>remove the respective case for <code class="docutils literal notranslate"><span class="pre">PYTHON_PKG_DEP</span></code></p></li>
</ol>
</li>
<li><p>remove the use of implementation flags from <code class="docutils literal notranslate"><span class="pre">profiles/</span></code> tree</p></li>
<li><p>remove the flags from <code class="docutils literal notranslate"><span class="pre">profiles/desc/python_targets.desc</span></code>
and <code class="docutils literal notranslate"><span class="pre">profiles/desc/python_single_target.desc</span></code></p></li>
<li><p>set the implementation status to <code class="docutils literal notranslate"><span class="pre">dead</span></code>
in <code class="docutils literal notranslate"><span class="pre">app-portage/gpyutils/files/implementations.txt</span></code></p></li>
<li><p>update the <a class="reference external" href="https://wiki.gentoo.org/wiki/Project:Python/Implementations">implementation tables</a> on Gentoo wiki</p></li>
</ul>
</section>
</section>
<section id="python-build-system-bootstrap">
<h2>Python build system bootstrap<a class="headerlink" href="#python-build-system-bootstrap" title="Link to this heading">¶</a></h2>
<p>Python build systems are often facing the bootstrap problem — that is,
the build system itself has some dependencies, while these dependencies
require the same build system to build. The common upstream way
(actually recommended in <a class="reference external" href="https://www.python.org/dev/peps/pep-0517/#build-requirements">PEP 517 build requirements</a> section) is
to bundle the necessary dependencies as part of the build system.
However, this goes against best Gentoo practices.</p>
<p>The current Gentoo practice for bootstrap with dependency unbundling
is to:</p>
<ol class="arabic simple">
<li><p>Install the dependencies of flit_core and the eclass PEP 517 logic
(installer, tomli) manually using <code class="docutils literal notranslate"><span class="pre">python_domodule</span></code>.</p></li>
<li><p>Install flit_core using the standalone PEP 517 backend.</p></li>
<li><p>Install the dependencies of setuptools using flit (writing trivial
<code class="docutils literal notranslate"><span class="pre">pyproject.toml</span></code> within the ebuild if necessary).</p></li>
<li><p>Install setuptools using the standalone PEP 517 backend.</p></li>
<li><p>The dependencies of other build systems can be installed using
flit, setuptools or other previously unbundled build systems.</p></li>
</ol>
<p>Note that for the purpose of bootstrap only obligatory baseline
dependencies are considered significant. Non-obligatory dependencies
(i.e. ones that can be missing during the bootstrap process) can be
placed in <code class="docutils literal notranslate"><span class="pre">PDEPEND</span></code>. Test suite dependencies can include cycles
with the package itself — running tests is not considered obligatory
during the bootstrap process.</p>
<p>flit_core has been chosen as the base build system for unbundling since
it has the fewest external dependencies (i.e. only depends on tomli).
Its author indicates in the <a class="reference external" href="https://github.com/pypa/flit/blob/main/flit_core/flit_core/vendor/README">flit_core vendoring README</a> that no other
dependencies will be added or vendored into flit_core.</p>
</section>
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