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<section id="pep-content">
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<h1 class="page-title">PEP 641 – Using an underscore in the version portion of Python 3.10 compatibility tags</h1>
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<dl class="rfc2822 field-list simple">
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<dt class="field-odd">Author<span class="colon">:</span></dt>
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<dd class="field-odd">Brett Cannon <brett at python.org>,
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Steve Dower <steve.dower at python.org>,
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Barry Warsaw <barry at python.org></dd>
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<dt class="field-even">PEP-Delegate<span class="colon">:</span></dt>
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<dd class="field-even">Pablo Galindo <pablogsal at python.org></dd>
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<dt class="field-odd">Discussions-To<span class="colon">:</span></dt>
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<dd class="field-odd"><a class="reference external" href="https://discuss.python.org/t/pep-641-using-an-underscore-in-the-version-portion-of-python-3-10-compatibility-tags/5513">Discourse thread</a></dd>
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<dt class="field-even">Status<span class="colon">:</span></dt>
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<dd class="field-even"><abbr title="Formally declined and will not be accepted">Rejected</abbr></dd>
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<dt class="field-odd">Type<span class="colon">:</span></dt>
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<dd class="field-odd"><abbr title="Normative PEP with a new feature for Python, implementation change for CPython or interoperability standard for the ecosystem">Standards Track</abbr></dd>
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<dt class="field-even">Created<span class="colon">:</span></dt>
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<dd class="field-even">20-Oct-2020</dd>
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<dt class="field-odd">Python-Version<span class="colon">:</span></dt>
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<dd class="field-odd">3.10</dd>
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<dt class="field-even">Post-History<span class="colon">:</span></dt>
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<dd class="field-even">21-Oct-2020</dd>
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<dt class="field-odd">Resolution<span class="colon">:</span></dt>
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<dd class="field-odd"><a class="reference external" href="https://discuss.python.org/t/pep-641-using-an-underscore-in-the-version-portion-of-python-3-10-compatibility-tags/5513/42">Discourse message</a></dd>
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</dl>
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<hr class="docutils" />
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<section id="contents">
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<details><summary>Table of Contents</summary><ul class="simple">
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<li><a class="reference internal" href="#abstract">Abstract</a></li>
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<li><a class="reference internal" href="#motivation">Motivation</a></li>
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<li><a class="reference internal" href="#rationale">Rationale</a></li>
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<li><a class="reference internal" href="#specification">Specification</a></li>
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<li><a class="reference internal" href="#backwards-compatibility">Backwards Compatibility</a></li>
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<li><a class="reference internal" href="#security-implications">Security Implications</a></li>
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<li><a class="reference internal" href="#how-to-teach-this">How to Teach This</a></li>
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<li><a class="reference internal" href="#reference-implementation">Reference Implementation</a></li>
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<li><a class="reference internal" href="#rejected-ideas">Rejected Ideas</a><ul>
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<li><a class="reference internal" href="#not-making-the-change">Not making the change</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#open-issues">Open Issues</a><ul>
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<li><a class="reference internal" href="#how-far-should-we-take-this">How far should we take this?</a></li>
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<li><a class="reference internal" href="#standardizing-on-double-digit-minor-version-numbers">Standardizing on double digit minor version numbers</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#references">References</a></li>
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<li><a class="reference internal" href="#copyright">Copyright</a></li>
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</ul>
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</details></section>
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<section id="abstract">
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<h2><a class="toc-backref" href="#abstract" role="doc-backlink">Abstract</a></h2>
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<div class="admonition note">
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<p class="admonition-title">Note</p>
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<p>This PEP was rejected due to potential breakage in the community.</p>
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</div>
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<p>Using the tag system outlined in <a class="pep reference internal" href="../pep-0425/" title="PEP 425 – Compatibility Tags for Built Distributions">PEP 425</a> (primarily used for wheel
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file names), each release of Python specifies compatibility tags
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(e.g. <code class="docutils literal notranslate"><span class="pre">cp39</span></code>, <code class="docutils literal notranslate"><span class="pre">py39</span></code> for CPython 3.9). For CPython 3.10, this PEP
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proposes using <code class="docutils literal notranslate"><span class="pre">3_10</span></code> as the version portion of the tags
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(instead of <code class="docutils literal notranslate"><span class="pre">310</span></code>).</p>
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</section>
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<section id="motivation">
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<h2><a class="toc-backref" href="#motivation" role="doc-backlink">Motivation</a></h2>
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<p>Up to this point, the version portion of compatibility tags used in
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e.g. wheel file names has been a straight concatenation of the major
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||
and minor versions of Python, both for the CPython interpreter tag and
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the generic, interpreter-agnostic interpreter tag (e.g. <code class="docutils literal notranslate"><span class="pre">cp39</span></code> and
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<code class="docutils literal notranslate"><span class="pre">py39</span></code>, respectively). This also applies to the ABI tag
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(e.g. <code class="docutils literal notranslate"><span class="pre">cp39</span></code>). Thanks to both the major and minor versions being
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single digits, it has been unambiguous what which digit in e.g. <code class="docutils literal notranslate"><span class="pre">39</span></code>
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represented.</p>
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<p>But starting with Python 3.10, ambiguity comes up as <code class="docutils literal notranslate"><span class="pre">310</span></code> does not
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||
clearly delineate whether the Python version is <code class="docutils literal notranslate"><span class="pre">3.10</span></code>, <code class="docutils literal notranslate"><span class="pre">31.0</span></code>, or
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||
<code class="docutils literal notranslate"><span class="pre">310</span></code> as the major-only version of Python. Thus using <code class="docutils literal notranslate"><span class="pre">3_10</span></code> to
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||
separate major/minor portions as allowed by <a class="pep reference internal" href="../pep-0425/" title="PEP 425 – Compatibility Tags for Built Distributions">PEP 425</a> disambiguates
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||
the Python version being supported.</p>
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</section>
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<section id="rationale">
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||
<h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2>
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||
<p>Using <code class="docutils literal notranslate"><span class="pre">3_10</span></code> instead of another proposed separator is a restriction
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||
of <a class="pep reference internal" href="../pep-0425/" title="PEP 425 – Compatibility Tags for Built Distributions">PEP 425</a>, thus the only options are <code class="docutils literal notranslate"><span class="pre">3_10</span></code> or <code class="docutils literal notranslate"><span class="pre">310</span></code>.</p>
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||
</section>
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||
<section id="specification">
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||
<h2><a class="toc-backref" href="#specification" role="doc-backlink">Specification</a></h2>
|
||
<p>The <code class="docutils literal notranslate"><span class="pre">SOABI</span></code> configure variable and
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||
<code class="docutils literal notranslate"><span class="pre">sysconfig.get_config_var('py_version_nodot')</span></code> will be updated to
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||
use <code class="docutils literal notranslate"><span class="pre">3_10</span></code> appropriately.</p>
|
||
</section>
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||
<section id="backwards-compatibility">
|
||
<h2><a class="toc-backref" href="#backwards-compatibility" role="doc-backlink">Backwards Compatibility</a></h2>
|
||
<p>Tools relying on the ‘packaging’ project <a class="footnote-reference brackets" href="#id4" id="id1">[2]</a> already expect a
|
||
version specification of <code class="docutils literal notranslate"><span class="pre">3_10</span></code> for Python 3.10. Keeping the version
|
||
specifier as <code class="docutils literal notranslate"><span class="pre">310</span></code> would require backing that change out and
|
||
updating dependent projects (e.g. pip).</p>
|
||
<p>Switching to <code class="docutils literal notranslate"><span class="pre">3_10</span></code> will impact any tools that implicitly rely on
|
||
the convention that the minor version is a single digit. However,
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||
these are broken regardless of any change here.</p>
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||
<p>For tools assuming the major version is only the first digit, they
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||
will require updating if we switch to <code class="docutils literal notranslate"><span class="pre">3_10</span></code>.</p>
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||
<p>In non-locale ASCII, <code class="docutils literal notranslate"><span class="pre">_</span></code> sorts after any digit, so lexicographic
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||
sorting matching a sort by Python version of a wheel file name will be
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kept.</p>
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<p>Since <a class="pep reference internal" href="../pep-0515/" title="PEP 515 – Underscores in Numeric Literals">PEP 515</a> (Python 3.6), underscores in numeric literals are ignored.
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||
This means that <code class="docutils literal notranslate"><span class="pre">int("3_10")</span></code> and <code class="docutils literal notranslate"><span class="pre">int("310")</span></code> produce the same result,
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and ordering based on conversion to an integer will be preserved.
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<strong>However</strong>, this is still a bad way to sort tags, and the point is raised
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||
here simply to show that this proposal does not make things worse.</p>
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||
</section>
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<section id="security-implications">
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<h2><a class="toc-backref" href="#security-implications" role="doc-backlink">Security Implications</a></h2>
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<p>There are no known security concerns.</p>
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</section>
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<section id="how-to-teach-this">
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<h2><a class="toc-backref" href="#how-to-teach-this" role="doc-backlink">How to Teach This</a></h2>
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<p>As use of the interpreter tag is mostly machine-based and this PEP
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disambiguates, there should not be any special teaching consideration
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required.</p>
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</section>
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<section id="reference-implementation">
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<h2><a class="toc-backref" href="#reference-implementation" role="doc-backlink">Reference Implementation</a></h2>
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<p>A pull request <a class="footnote-reference brackets" href="#id3" id="id2">[1]</a> already exists adding support to CPython 3.10.
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Support for reading wheel files with this proposed PEP is already
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implemented.</p>
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</section>
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<section id="rejected-ideas">
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<h2><a class="toc-backref" href="#rejected-ideas" role="doc-backlink">Rejected Ideas</a></h2>
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<section id="not-making-the-change">
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<h3><a class="toc-backref" href="#not-making-the-change" role="doc-backlink">Not making the change</a></h3>
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<p>It was considered to not change the tag and stay with <code class="docutils literal notranslate"><span class="pre">310</span></code>. The
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argument was it’s less work and it won’t break any existing
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tooling. But in the end it was thought that the disambiguation is
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better to have.</p>
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</section>
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</section>
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<section id="open-issues">
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<h2><a class="toc-backref" href="#open-issues" role="doc-backlink">Open Issues</a></h2>
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||
<section id="how-far-should-we-take-this">
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<h3><a class="toc-backref" href="#how-far-should-we-take-this" role="doc-backlink">How far should we take this?</a></h3>
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<p>Other places where the major and minor version are used could be
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updated to use an underscore as well (e.g. <code class="docutils literal notranslate"><span class="pre">.pyc</span></code> files, the import
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path to the zip file for the stdlib). It is not known how useful it
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would be to make this pervasive.</p>
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</section>
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<section id="standardizing-on-double-digit-minor-version-numbers">
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<h3><a class="toc-backref" href="#standardizing-on-double-digit-minor-version-numbers" role="doc-backlink">Standardizing on double digit minor version numbers</a></h3>
|
||
<p>An alternative suggestion has been made to disambiguate where the
|
||
major and minor versions start/stop by forcing the minor version to
|
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always be two digits, padding with a <code class="docutils literal notranslate"><span class="pre">0</span></code> as required. The advantages
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of this is it makes the current <code class="docutils literal notranslate"><span class="pre">cp310</span></code> interpreter tag accurate,
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thus minimizing breakage. It also does differentiate going forward.</p>
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<p>There are a couple of drawbacks, though. One is the disambiguation
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only exists <em>if</em> you know that the minor version number is two digits;
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compare that to <code class="docutils literal notranslate"><span class="pre">cp3_10</span></code> which is unambiguous regardless of your
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base knowledge. The potential for a three digit minor version number
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is also not addressed by this two digit requirement.</p>
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<p>There is also the issue of other interpreters not following the
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practice in the past, present, or future. For instance, it is
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unknown if other people have used a three digit version portion of the
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interpreter tag previously for another interpreter where this rule
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would be incorrect. This change would also suggest that interpreters which
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currently have a single digit minor version – e.g. PyPy 7.3 – to
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change from <code class="docutils literal notranslate"><span class="pre">pp73</span></code> to <code class="docutils literal notranslate"><span class="pre">pp703</span></code> or make the switch from their next
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||
minor release onward (e.g. 7.4 or 8.0). Otherwise this would make this
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rule exclusive to the <code class="docutils literal notranslate"><span class="pre">cp</span></code> interpreter type which would make it more
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confusing for people.</p>
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</section>
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</section>
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<section id="references">
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<h2><a class="toc-backref" href="#references" role="doc-backlink">References</a></h2>
|
||
<aside class="footnote-list brackets">
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<aside class="footnote brackets" id="id3" role="doc-footnote">
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<dt class="label" id="id3">[<a href="#id2">1</a>]</dt>
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<dd>Reference implementation
|
||
(<a class="reference external" href="https://github.com/python/cpython/pull/20333">https://github.com/python/cpython/pull/20333</a>)</aside>
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<aside class="footnote brackets" id="id4" role="doc-footnote">
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<dt class="label" id="id4">[<a href="#id1">2</a>]</dt>
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<dd>The ‘packaging’ project
|
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(<a class="reference external" href="https://pypi.org/project/packaging/">https://pypi.org/project/packaging/</a>)</aside>
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</aside>
|
||
</section>
|
||
<section id="copyright">
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||
<h2><a class="toc-backref" href="#copyright" role="doc-backlink">Copyright</a></h2>
|
||
<p>This document is placed in the public domain or under the
|
||
CC0-1.0-Universal license, whichever is more permissive.</p>
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||
</section>
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||
</section>
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||
<hr class="docutils" />
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||
<p>Source: <a class="reference external" href="https://github.com/python/peps/blob/main/peps/pep-0641.rst">https://github.com/python/peps/blob/main/peps/pep-0641.rst</a></p>
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<p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0641.rst">2023-09-09 17:39:29 GMT</a></p>
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||
|
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</article>
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||
<nav id="pep-sidebar">
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||
<h2>Contents</h2>
|
||
<ul>
|
||
<li><a class="reference internal" href="#abstract">Abstract</a></li>
|
||
<li><a class="reference internal" href="#motivation">Motivation</a></li>
|
||
<li><a class="reference internal" href="#rationale">Rationale</a></li>
|
||
<li><a class="reference internal" href="#specification">Specification</a></li>
|
||
<li><a class="reference internal" href="#backwards-compatibility">Backwards Compatibility</a></li>
|
||
<li><a class="reference internal" href="#security-implications">Security Implications</a></li>
|
||
<li><a class="reference internal" href="#how-to-teach-this">How to Teach This</a></li>
|
||
<li><a class="reference internal" href="#reference-implementation">Reference Implementation</a></li>
|
||
<li><a class="reference internal" href="#rejected-ideas">Rejected Ideas</a><ul>
|
||
<li><a class="reference internal" href="#not-making-the-change">Not making the change</a></li>
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||
</ul>
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<li><a class="reference internal" href="#open-issues">Open Issues</a><ul>
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|
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<li><a class="reference internal" href="#standardizing-on-double-digit-minor-version-numbers">Standardizing on double digit minor version numbers</a></li>
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