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<h1>Python Enhancement Proposals</h1>
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<section id="pep-content">
<h1 class="page-title">PEP 390 – Static metadata for Distutils</h1>
<dl class="rfc2822 field-list simple">
<dt class="field-odd">Author<span class="colon">:</span></dt>
<dd class="field-odd">Tarek Ziadé &lt;tarek&#32;&#97;t&#32;ziade.org&gt;</dd>
<dt class="field-even">BDFL-Delegate<span class="colon">:</span></dt>
<dd class="field-even">Alyssa Coghlan</dd>
<dt class="field-odd">Discussions-To<span class="colon">:</span></dt>
<dd class="field-odd"><a class="reference external" href="https://mail.python.org/archives/list/distutils-sig&#64;python.org/">Distutils-SIG list</a></dd>
<dt class="field-even">Status<span class="colon">:</span></dt>
<dd class="field-even"><abbr title="Formally declined and will not be accepted">Rejected</abbr></dd>
<dt class="field-odd">Type<span class="colon">:</span></dt>
<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>
<dt class="field-even">Topic<span class="colon">:</span></dt>
<dd class="field-even"><a class="reference external" href="../topic/packaging/">Packaging</a></dd>
<dt class="field-odd">Created<span class="colon">:</span></dt>
<dd class="field-odd">10-Oct-2009</dd>
<dt class="field-even">Python-Version<span class="colon">:</span></dt>
<dd class="field-even">2.7, 3.2</dd>
<dt class="field-odd">Post-History<span class="colon">:</span></dt>
<dd class="field-odd"><p></p></dd>
<dt class="field-even">Resolution<span class="colon">:</span></dt>
<dd class="field-even"><a class="reference external" href="https://mail.python.org/pipermail/distutils-sig/2013-April/020597.html">Distutils-SIG message</a></dd>
</dl>
<hr class="docutils" />
<section id="contents">
<details><summary>Table of Contents</summary><ul class="simple">
<li><a class="reference internal" href="#abstract">Abstract</a></li>
<li><a class="reference internal" href="#rejection-notice">Rejection Notice</a></li>
<li><a class="reference internal" href="#rationale">Rationale</a></li>
<li><a class="reference internal" href="#adding-a-metadata-section-in-setup-cfg">Adding a <code class="docutils literal notranslate"><span class="pre">metadata</span></code> section in <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code></a></li>
<li><a class="reference internal" href="#multi-lines-values">Multi-lines values</a></li>
<li><a class="reference internal" href="#context-dependant-sections">Context-dependant sections</a></li>
<li><a class="reference internal" href="#impact-on-pkg-info-generation-and-pep-314">Impact on PKG-INFO generation and PEP 314</a></li>
<li><a class="reference internal" href="#compatibility">Compatibility</a></li>
<li><a class="reference internal" href="#limitations">Limitations</a></li>
<li><a class="reference internal" href="#acknowledgments">Acknowledgments</a></li>
<li><a class="reference internal" href="#copyright">Copyright</a></li>
</ul>
</details></section>
<section id="abstract">
<h2><a class="toc-backref" href="#abstract" role="doc-backlink">Abstract</a></h2>
<p>This PEP describes a new section and a new format for the <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code> file,
that allows describing the Metadata of a package without using <code class="docutils literal notranslate"><span class="pre">setup.py</span></code>.</p>
</section>
<section id="rejection-notice">
<h2><a class="toc-backref" href="#rejection-notice" role="doc-backlink">Rejection Notice</a></h2>
<p>As distutils2 is no longer going to be incorporated into the standard
library, this PEP was rejected by Alyssa Coghlan in late April, 2013.</p>
<p>A replacement PEP based on <a class="pep reference internal" href="../pep-0426/" title="PEP 426 – Metadata for Python Software Packages 2.0">PEP 426</a> (metadata 2.0) will be created that
defines the minimum amount of information needed to generate an sdist
archive given a source tarball or VCS checkout.</p>
</section>
<section id="rationale">
<h2><a class="toc-backref" href="#rationale" role="doc-backlink">Rationale</a></h2>
<p>Today, if you want to list all the Metadata of a distribution (see <a class="pep reference internal" href="../pep-0314/" title="PEP 314 – Metadata for Python Software Packages 1.1">PEP 314</a>)
that is not installed, you need to use the <code class="docutils literal notranslate"><span class="pre">setup.py</span></code> command line interface.</p>
<p>So, basically, you download it, and run:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ python setup.py --name
Distribute
$ python setup.py --version
0.6.4
</pre></div>
</div>
<p>Where <code class="docutils literal notranslate"><span class="pre">name</span></code> and <code class="docutils literal notranslate"><span class="pre">version</span></code> are metadata fields. This is working fine but
as soon as the developers add more code in <code class="docutils literal notranslate"><span class="pre">setup.py</span></code>, this feature might
break or in worst cases might do unwanted things on the target system.</p>
<p>Moreover, when an OS packager wants to get the metadata of a distribution
he is re-packaging, he might encounter some problems to understand
the <code class="docutils literal notranslate"><span class="pre">setup.py</span></code> file he’s working with.</p>
<p>So the rationale of this PEP is to provide a way to declare the metadata
in a static configuration file alongside <code class="docutils literal notranslate"><span class="pre">setup.py</span></code> that doesn’t require
any third party code to run.</p>
</section>
<section id="adding-a-metadata-section-in-setup-cfg">
<h2><a class="toc-backref" href="#adding-a-metadata-section-in-setup-cfg" role="doc-backlink">Adding a <code class="docutils literal notranslate"><span class="pre">metadata</span></code> section in <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code></a></h2>
<p>The first thing we want to introduce is a <code class="docutils literal notranslate"><span class="pre">[metadata]</span></code> section, in the
<code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code> file, that may contain any field from the Metadata:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">metadata</span><span class="p">]</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">Distribute</span>
<span class="n">version</span> <span class="o">=</span> <span class="mf">0.6.4</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code> file is used to avoid adding yet another configuration
file to work with in Distutils.</p>
<p>This file is already read by Distutils when a command is executed, and
if the <code class="docutils literal notranslate"><span class="pre">metadata</span></code> section is found, it will be used to fill the metadata
fields. If an option that corresponds to a Metadata field is given to
<code class="docutils literal notranslate"><span class="pre">setup()</span></code>, it will override the value that was possibly present in
<code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code>.</p>
<p>Notice that <code class="docutils literal notranslate"><span class="pre">setup.py</span></code> is still used and can be required to define some
options that are not part of the Metadata fields. For instance, the
<code class="docutils literal notranslate"><span class="pre">sdist</span></code> command can use options like <code class="docutils literal notranslate"><span class="pre">packages</span></code> or <code class="docutils literal notranslate"><span class="pre">scripts</span></code>.</p>
</section>
<section id="multi-lines-values">
<h2><a class="toc-backref" href="#multi-lines-values" role="doc-backlink">Multi-lines values</a></h2>
<p>Some Metadata fields can have multiple values. To keep <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code> compatible
with <code class="docutils literal notranslate"><span class="pre">ConfigParser</span></code> and the <span class="target" id="index-0"></span><a class="rfc reference external" href="https://datatracker.ietf.org/doc/html/rfc822.html"><strong>RFC 822</strong></a> <code class="docutils literal notranslate"><span class="pre">LONG</span> <span class="pre">HEADER</span> <span class="pre">FIELDS</span></code> (see section 3.1.1),
these are expressed with <code class="docutils literal notranslate"><span class="pre">,</span></code>-separated values:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">requires</span> <span class="o">=</span> <span class="n">pywin32</span><span class="p">,</span> <span class="n">bar</span> <span class="o">&gt;</span> <span class="mf">1.0</span><span class="p">,</span> <span class="n">foo</span>
</pre></div>
</div>
<p>When this variable is read, the values are parsed and transformed into a list:
<code class="docutils literal notranslate"><span class="pre">['pywin32',</span> <span class="pre">'bar</span> <span class="pre">&gt;</span> <span class="pre">1.0',</span> <span class="pre">'foo']</span></code>.</p>
</section>
<section id="context-dependant-sections">
<h2><a class="toc-backref" href="#context-dependant-sections" role="doc-backlink">Context-dependant sections</a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">metadata</span></code> section will also be able to use context-dependant sections.</p>
<p>A context-dependant section is a section with a condition about the execution
environment. Here’s some examples:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">metadata</span><span class="p">]</span>
<span class="n">name</span> <span class="o">=</span> <span class="n">Distribute</span>
<span class="n">version</span> <span class="o">=</span> <span class="mf">0.6.4</span>
<span class="p">[</span><span class="n">metadata</span><span class="p">:</span><span class="n">sys_platform</span> <span class="o">==</span> <span class="s1">&#39;win32&#39;</span><span class="p">]</span>
<span class="n">requires</span> <span class="o">=</span> <span class="n">pywin32</span><span class="p">,</span> <span class="n">bar</span> <span class="o">&gt;</span> <span class="mf">1.0</span>
<span class="n">obsoletes</span> <span class="o">=</span> <span class="n">pywin31</span>
<span class="p">[</span><span class="n">metadata</span><span class="p">:</span><span class="n">os_machine</span> <span class="o">==</span> <span class="s1">&#39;i386&#39;</span><span class="p">]</span>
<span class="n">requires</span> <span class="o">=</span> <span class="n">foo</span>
<span class="p">[</span><span class="n">metadata</span><span class="p">:</span><span class="n">python_version</span> <span class="o">==</span> <span class="s1">&#39;2.4&#39;</span> <span class="ow">or</span> <span class="n">python_version</span> <span class="o">==</span> <span class="s1">&#39;2.5&#39;</span><span class="p">]</span>
<span class="n">requires</span> <span class="o">=</span> <span class="n">bar</span>
<span class="p">[</span><span class="n">metadata</span><span class="p">:</span><span class="s1">&#39;linux&#39;</span> <span class="ow">in</span> <span class="n">sys_platform</span><span class="p">]</span>
<span class="n">requires</span> <span class="o">=</span> <span class="n">baz</span>
</pre></div>
</div>
<p>Every <code class="docutils literal notranslate"><span class="pre">[metadata:condition]</span></code> section will be used only if the condition
is met when the file is read. The background motivation for these
context-dependant sections is to be able to define requirements that varies
depending on the platform the distribution might be installed on.
(see <a class="pep reference internal" href="../pep-0314/" title="PEP 314 – Metadata for Python Software Packages 1.1">PEP 314</a>).</p>
<p>The micro-language behind this is the simplest possible: it compares only
strings, with the <code class="docutils literal notranslate"><span class="pre">==</span></code> and <code class="docutils literal notranslate"><span class="pre">in</span></code> operators (and their opposites), and
with the ability to combine expressions. It makes it also easy to understand
to non-pythoneers.</p>
<p>The pseudo-grammar is</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">EXPR</span> <span class="p">[</span><span class="ow">in</span><span class="o">|==|!=|</span><span class="ow">not</span> <span class="ow">in</span><span class="p">]</span> <span class="n">EXPR</span> <span class="p">[</span><span class="ow">or</span><span class="o">|</span><span class="ow">and</span><span class="p">]</span> <span class="o">...</span>
</pre></div>
</div>
<p>where <code class="docutils literal notranslate"><span class="pre">EXPR</span></code> belongs to any of those:</p>
<ul class="simple">
<li>python_version = ‘%s.%s’ % (sys.version_info[0], sys.version_info[1])</li>
<li>os_name = os.name</li>
<li>sys_platform = sys.platform</li>
<li>platform_version = platform.version()</li>
<li>platform_machine = platform.machine()</li>
<li>a free string, like <code class="docutils literal notranslate"><span class="pre">2.4</span></code>, or <code class="docutils literal notranslate"><span class="pre">win32</span></code></li>
</ul>
<p>Notice that <code class="docutils literal notranslate"><span class="pre">in</span></code> is restricted to strings, meaning that it is not possible
to use other sequences like tuples or lists on the right side.</p>
<p>Distutils will provide a function that is able to generate the metadata
of a distribution, given a <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code> file, for the execution environment:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">distutils.util</span> <span class="kn">import</span> <span class="n">local_metadata</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">local_metadata</span><span class="p">(</span><span class="s1">&#39;setup.cfg&#39;</span><span class="p">)</span>
<span class="go">&lt;DistributionMetadata instance&gt;</span>
</pre></div>
</div>
<p>This means that a vanilla Python will be able to read the metadata of a
package without running any third party code.</p>
<p>Notice that this feature is not restricted to the <code class="docutils literal notranslate"><span class="pre">metadata</span></code> namespace.
Consequently, any other section can be extended with such context-dependant
sections.</p>
</section>
<section id="impact-on-pkg-info-generation-and-pep-314">
<h2><a class="toc-backref" href="#impact-on-pkg-info-generation-and-pep-314" role="doc-backlink">Impact on PKG-INFO generation and PEP 314</a></h2>
<p>When <code class="docutils literal notranslate"><span class="pre">PKG-INFO</span></code> is generated by Distutils, every field that relies on a
condition will have that condition written at the end of the line, after a
<code class="docutils literal notranslate"><span class="pre">;</span></code> separator:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Metadata</span><span class="o">-</span><span class="n">Version</span><span class="p">:</span> <span class="mf">1.2</span>
<span class="n">Name</span><span class="p">:</span> <span class="n">distribute</span>
<span class="n">Version</span><span class="p">:</span> <span class="mf">0.6.4</span>
<span class="o">...</span>
<span class="n">Requires</span><span class="p">:</span> <span class="n">pywin32</span><span class="p">,</span> <span class="n">bar</span> <span class="o">&gt;</span> <span class="mf">1.0</span><span class="p">;</span> <span class="n">sys_platform</span> <span class="o">==</span> <span class="s1">&#39;win32&#39;</span>
<span class="n">Requires</span><span class="p">:</span> <span class="n">foo</span><span class="p">;</span> <span class="n">os_machine</span> <span class="o">==</span> <span class="s1">&#39;i386&#39;</span>
<span class="n">Requires</span><span class="p">:</span> <span class="n">bar</span><span class="p">;</span> <span class="n">python_version</span> <span class="o">==</span> <span class="s1">&#39;2.4&#39;</span> <span class="ow">or</span> <span class="n">python_version</span> <span class="o">==</span> <span class="s1">&#39;2.5&#39;</span>
<span class="n">Requires</span><span class="p">:</span> <span class="n">baz</span><span class="p">;</span> <span class="s1">&#39;linux&#39;</span> <span class="ow">in</span> <span class="n">sys_platform</span>
<span class="n">Obsoletes</span> <span class="o">=</span> <span class="n">pywin31</span><span class="p">;</span> <span class="n">sys_platform</span> <span class="o">==</span> <span class="s1">&#39;win32&#39;</span>
<span class="o">...</span>
<span class="n">Classifier</span><span class="p">:</span> <span class="n">Development</span> <span class="n">Status</span> <span class="p">::</span> <span class="mi">5</span> <span class="o">-</span> <span class="n">Production</span><span class="o">/</span><span class="n">Stable</span>
<span class="n">Classifier</span><span class="p">:</span> <span class="n">Intended</span> <span class="n">Audience</span> <span class="p">::</span> <span class="n">Developers</span>
<span class="n">Classifier</span><span class="p">:</span> <span class="n">License</span> <span class="p">::</span> <span class="n">OSI</span> <span class="n">Approved</span> <span class="p">::</span> <span class="n">Python</span> <span class="n">Software</span> <span class="n">Foundation</span> <span class="n">License</span>
</pre></div>
</div>
<p>Notice that this file can be opened with the <code class="docutils literal notranslate"><span class="pre">DistributionMetadata</span></code> class.
This class will be able to use the micro-language using the execution
environment.</p>
<p>Let’s run in on a <code class="docutils literal notranslate"><span class="pre">Python</span> <span class="pre">2.5</span> <span class="pre">i386</span> <span class="pre">Linux</span></code>:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">distutils.dist</span> <span class="kn">import</span> <span class="n">DistributionMetadata</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">metadata</span> <span class="o">=</span> <span class="n">DistributionMetadata</span><span class="p">(</span><span class="s1">&#39;PKG_INFO&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">metadata</span><span class="o">.</span><span class="n">get_requires</span><span class="p">()</span>
<span class="go">[&#39;foo&#39;, &#39;bar&#39;, &#39;baz&#39;]</span>
</pre></div>
</div>
<p>The execution environment can be overridden in case we want to get the metadata
for another environment:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">env</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;python_version&#39;</span><span class="p">:</span> <span class="s1">&#39;2.4&#39;</span><span class="p">,</span>
<span class="gp">... </span> <span class="s1">&#39;os_name&#39;</span><span class="p">:</span> <span class="s1">&#39;nt&#39;</span><span class="p">,</span>
<span class="gp">... </span> <span class="s1">&#39;sys_platform&#39;</span><span class="p">:</span> <span class="s1">&#39;win32&#39;</span><span class="p">,</span>
<span class="gp">... </span> <span class="s1">&#39;platform_version&#39;</span><span class="p">:</span> <span class="s1">&#39;MVCC++ 6.0&#39;</span>
<span class="gp">... </span> <span class="s1">&#39;platform_machine&#39;</span><span class="p">:</span> <span class="s1">&#39;i386&#39;</span><span class="p">}</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">metadata</span> <span class="o">=</span> <span class="n">DistributionMetadata</span><span class="p">(</span><span class="s1">&#39;PKG_INFO&#39;</span><span class="p">,</span> <span class="n">environment</span><span class="o">=</span><span class="n">env</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">metadata</span><span class="o">.</span><span class="n">get_requires</span><span class="p">()</span>
<span class="go">[&#39;bar &gt; 1.0&#39;, &#39;foo&#39;, &#39;bar&#39;]</span>
</pre></div>
</div>
<p><a class="pep reference internal" href="../pep-0314/" title="PEP 314 – Metadata for Python Software Packages 1.1">PEP 314</a> is changed accordingly, meaning that each field will be able to
have that extra condition marker.</p>
</section>
<section id="compatibility">
<h2><a class="toc-backref" href="#compatibility" role="doc-backlink">Compatibility</a></h2>
<p>This change is based on a new metadata <code class="docutils literal notranslate"><span class="pre">1.2</span></code> format meaning that
Distutils will be able to distinguish old PKG-INFO files from new ones.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code> file change will stay <code class="docutils literal notranslate"><span class="pre">ConfigParser</span></code>-compatible and
will not break existing <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code> files.</p>
</section>
<section id="limitations">
<h2><a class="toc-backref" href="#limitations" role="doc-backlink">Limitations</a></h2>
<p>We are not providing <code class="docutils literal notranslate"><span class="pre">&lt;</span></code> and <code class="docutils literal notranslate"><span class="pre">&gt;</span></code> operators at this time, and
<code class="docutils literal notranslate"><span class="pre">python_version</span></code> is a regular string. This implies using <code class="docutils literal notranslate"><span class="pre">or</span></code> operators
when a section needs to be restricted to a couple of Python versions.
Although, if <a class="pep reference internal" href="../pep-0386/" title="PEP 386 – Changing the version comparison module in Distutils">PEP 386</a> is accepted, <code class="docutils literal notranslate"><span class="pre">python_version</span></code> could be changed
internally into something comparable with strings, and
<code class="docutils literal notranslate"><span class="pre">&lt;</span></code> and <code class="docutils literal notranslate"><span class="pre">&gt;</span></code> operators introduced.</p>
<p>Last, if a distribution is unable to set all metadata fields in <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code>,
that’s fine, the fields will be set to <code class="docutils literal notranslate"><span class="pre">UNKNOWN</span></code> when <code class="docutils literal notranslate"><span class="pre">local_metadata</span></code> is
called. Getting <code class="docutils literal notranslate"><span class="pre">UNKNOWN</span></code> values will mean that it might be necessary to
run the <code class="docutils literal notranslate"><span class="pre">setup.py</span></code> command line interface to get the whole set of metadata.</p>
</section>
<section id="acknowledgments">
<h2><a class="toc-backref" href="#acknowledgments" role="doc-backlink">Acknowledgments</a></h2>
<p>The Distutils-SIG.</p>
</section>
<section id="copyright">
<h2><a class="toc-backref" href="#copyright" role="doc-backlink">Copyright</a></h2>
<p>This document has been placed in the public domain.</p>
</section>
</section>
<hr class="docutils" />
<p>Source: <a class="reference external" href="https://github.com/python/peps/blob/main/peps/pep-0390.rst">https://github.com/python/peps/blob/main/peps/pep-0390.rst</a></p>
<p>Last modified: <a class="reference external" href="https://github.com/python/peps/commits/main/peps/pep-0390.rst">2023-10-11 12:05:51 GMT</a></p>
</article>
<nav id="pep-sidebar">
<h2>Contents</h2>
<ul>
<li><a class="reference internal" href="#abstract">Abstract</a></li>
<li><a class="reference internal" href="#rejection-notice">Rejection Notice</a></li>
<li><a class="reference internal" href="#rationale">Rationale</a></li>
<li><a class="reference internal" href="#adding-a-metadata-section-in-setup-cfg">Adding a <code class="docutils literal notranslate"><span class="pre">metadata</span></code> section in <code class="docutils literal notranslate"><span class="pre">setup.cfg</span></code></a></li>
<li><a class="reference internal" href="#multi-lines-values">Multi-lines values</a></li>
<li><a class="reference internal" href="#context-dependant-sections">Context-dependant sections</a></li>
<li><a class="reference internal" href="#impact-on-pkg-info-generation-and-pep-314">Impact on PKG-INFO generation and PEP 314</a></li>
<li><a class="reference internal" href="#compatibility">Compatibility</a></li>
<li><a class="reference internal" href="#limitations">Limitations</a></li>
<li><a class="reference internal" href="#acknowledgments">Acknowledgments</a></li>
<li><a class="reference internal" href="#copyright">Copyright</a></li>
</ul>
<br>
<a id="source" href="https://github.com/python/peps/blob/main/peps/pep-0390.rst">Page Source (GitHub)</a>
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