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<section id="abstract">
<h1>Abstract<a class="headerlink" href="#abstract" title="Permalink to this heading">¶</a></h1>
<p>This document describes the packaging of Python within the Debian
GNU/Linux distribution and the policy requirements for packaged Python
programs and modules.</p>
</section>
<section id="contents">
<h1>Contents<a class="headerlink" href="#contents" title="Permalink to this heading">¶</a></h1>
<div class="toctree-wrapper compound">
<span id="document-copyright"></span><section id="copyright">
<h2><span class="section-number">1. </span>Copyright<a class="headerlink" href="#copyright" title="Permalink to this heading">¶</a></h2>
<p>1999-2021, Software in the Public Interest</p>
<dl class="simple">
<dt>Authors:</dt><dd><ul class="simple">
<li><p>Neil Schemenauer <<a class="reference external" href="mailto:nas%40debian.org">nas<span>@</span>debian<span>.</span>org</a>></p></li>
<li><p>Matthias Klose <<a class="reference external" href="mailto:doko%40debian.org">doko<span>@</span>debian<span>.</span>org</a>></p></li>
<li><p>Gregor Hoffleit <<a class="reference external" href="mailto:flight%40debian.org">flight<span>@</span>debian<span>.</span>org</a>></p></li>
<li><p>Josselin Mouette <<a class="reference external" href="mailto:joss%40debian.org">joss<span>@</span>debian<span>.</span>org</a>></p></li>
<li><p>Joe Wreschnig <<a class="reference external" href="mailto:piman%40debian.org">piman<span>@</span>debian<span>.</span>org</a>></p></li>
<li><p>Loïc Minier <<a class="reference external" href="mailto:lool%40debian.org">lool<span>@</span>debian<span>.</span>org</a>></p></li>
<li><p>Scott Kitterman <<a class="reference external" href="mailto:scott%40kitterman.com">scott<span>@</span>kitterman<span>.</span>com</a>></p></li>
<li><p>Barry Warsaw <<a class="reference external" href="mailto:barry%40debian.org">barry<span>@</span>debian<span>.</span>org</a>></p></li>
<li><p>Ben Finney <<a class="reference external" href="mailto:ben+debian%40benfinney.id.au">ben+debian<span>@</span>benfinney<span>.</span>id<span>.</span>au</a>></p></li>
<li><p>Neil Williams <<a class="reference external" href="mailto:codehelp%40debian.org">codehelp<span>@</span>debian<span>.</span>org</a>></p></li>
<li><p>Stefano Rivera <<a class="reference external" href="mailto:stefanor%40debian.org">stefanor<span>@</span>debian<span>.</span>org</a>></p></li>
</ul>
</dd>
</dl>
<p>This manual is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.</p>
<p>This is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.</p>
<p>A copy of the GNU General Public License version 2 is available as
<code class="file docutils literal notranslate"><span class="pre">/usr/share/common-licences/GPL-2</span></code> in the Debian GNU/Linux system,
or on the World Wide Web at <a class="reference external" href="https://www.gnu.org/licenses/old-licenses/gpl-2.0.html">GNU General Public License, version 2</a>.</p>
<p>You can also obtain it by writing to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.</p>
</section>
<span id="document-python3"></span><section id="completing-the-move-to-python-3">
<h2><span class="section-number">2. </span>Completing the move to Python 3<a class="headerlink" href="#completing-the-move-to-python-3" title="Permalink to this heading">¶</a></h2>
<p>Debian has previously supported two Python stacks, one for Python 3 and
one for Python 2.
The goal for Debian is to reduce this to one stack, dropping the Python
2 stack and interpreter for the Bullseye release.</p>
<p><span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0404/"><strong>PEP 404</strong></a> states that no more major Python 2 releases are planned,
although the latest released minor version 2.7 will see some extended
support, documented in <span class="target" id="index-1"></span><a class="pep reference external" href="https://peps.python.org/pep-0466/"><strong>PEP 466</strong></a>.</p>
<p>Packages in Debian should use Python 3.
New packages must use Python 3 from the initial upload, new upstream
versions for existing packages must use Python 3.
If Python 2 is still supported in Bullseye, selected packages may
continue using Python 2 until Python 3 support is available for those
packages.
Please discuss all use of Python 2 on the debian-python mailing list
before uploading.</p>
<ol class="arabic simple">
<li><p>Applications should use Python 3 and must not be packaged for Python
2 as well.
If an application supports only Python 2, the application may need
to be removed from Debian so that it does not block removal of other
Python 2 packages.</p></li>
<li><p>Python libraries need to support Python 3 and new versions must be
packaged for Python 3.
Existing Python 2 libraries must not be dropped before the last
reverse dependency is removed.
New Python 2 libraries must not be introduced.</p></li>
<li><p>Python 3 should be used for the packaging if the packaging scripts
use Python.</p></li>
</ol>
<section id="removal-of-the-unversioned-packages">
<h3><span class="section-number">2.1. </span>Removal of the unversioned packages<a class="headerlink" href="#removal-of-the-unversioned-packages" title="Permalink to this heading">¶</a></h3>
<p>Starting with the Debian 11 release (bullseye), the binary packages
<code class="docutils literal notranslate"><span class="pre">python</span></code>, <code class="docutils literal notranslate"><span class="pre">python-minimal</span></code>, <code class="docutils literal notranslate"><span class="pre">python-dev</span></code>, <code class="docutils literal notranslate"><span class="pre">python-dbg</span></code> and
<code class="docutils literal notranslate"><span class="pre">python-doc</span></code> are removed. No package in the archive must use any of
these packages as build dependencies, dependencies, recommendations or
suggestions.</p>
</section>
<section id="unversioned-python-commands">
<h3><span class="section-number">2.2. </span>Unversioned python commands<a class="headerlink" href="#unversioned-python-commands" title="Permalink to this heading">¶</a></h3>
<p>For the Debian 11 release (bullseye), the <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python</span></code>
command is provided in the <code class="docutils literal notranslate"><span class="pre">python-is-python2</span></code> package (pointing to
<code class="file docutils literal notranslate"><span class="pre">/usr/bin/python2</span></code>). The <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python-config</span></code> and
<code class="file docutils literal notranslate"><span class="pre">/usr/bin/pydoc</span></code> commands are provided in the
<code class="docutils literal notranslate"><span class="pre">python-dev-is-python2</span></code> package. These package are not installed by
default for new installations, but only for upgrades from the Debian
10 release (buster). These packages should be removed after an
upgrade. These packages will not be part of the Debian 12 release
(bookworm).</p>
<p>The packages <code class="docutils literal notranslate"><span class="pre">python-is-python3</span></code> and <code class="docutils literal notranslate"><span class="pre">python-dev-is-python3</span></code>
provide the <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python</span></code>, <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python-config</span></code>
and <code class="file docutils literal notranslate"><span class="pre">/usr/bin/pydoc</span></code> commands pointing to Python3. These
packages can be installed by developers and users to use the
unversioned commands. NOTE: Locally installed software not yet ported
to Python3 is likely to break when installing these packages.</p>
<p>The packages <code class="docutils literal notranslate"><span class="pre">python-is-python3</span></code>, <code class="docutils literal notranslate"><span class="pre">python-dev-is-python3</span></code>,
<code class="docutils literal notranslate"><span class="pre">python-is-python2</span></code> and <code class="docutils literal notranslate"><span class="pre">python-dev-is-python2</span></code> must not be used
as build dependencies, dependencies, recommendations or suggestions.</p>
</section>
</section>
<span id="document-interpreter"></span><section id="python-packaging">
<h2><span class="section-number">3. </span>Python Packaging<a class="headerlink" href="#python-packaging" title="Permalink to this heading">¶</a></h2>
<section id="versions">
<h3><span class="section-number">3.1. </span>Versions<a class="headerlink" href="#versions" title="Permalink to this heading">¶</a></h3>
<p>At any given time, the binary package <code class="docutils literal notranslate"><span class="pre">python3</span></code> will represent the
current default Debian Python 3 version; the binary package <code class="docutils literal notranslate"><span class="pre">python</span></code>
will represent the current default Debian Python 2 version, for as long
as it exists.
As far as is reasonable, Python 3 and Python 2 should be treated as
separate runtime systems with minimal interdependencies.</p>
<p>In some cases, Python policy explicitly references Python helper tools.
For Debian Stretch, the <code class="docutils literal notranslate"><span class="pre">dh-python</span></code> package provides the only such
tools; earlier helpers have been removed from Debian.</p>
<p>It is a design goal to fully specify required interfaces and functions
in policy for Python 3 and to avoid enshrining specific implementation
details in policy.
Except as noted, policy for Python 2 is the same as Python 3 with the
exception of the different major version number as needed to distinguish
them.</p>
<p>The default Debian Python version, for each of Python 3 and Python 2,
should always be the latest stable upstream version that can be fully
integrated in Debian.</p>
<p>There may be newer supported or unsupported versions included in Debian
if they are not fully integrated for a particular release.</p>
<p>Apart from the default version, legacy versions of Python or beta
releases of future upstream versions may be included as well in Debian,
as long as they are needed by other packages, or as long as it seems
reasonable to provide them.</p>
<p>Note: For the scope of this document, a Python version is synonymous
with all micro versions within that minor version.
e.g. Python 3.5.0 and 3.5.1 are micro versions of the same Python
version 3.5, but Python 3.4 and 3.5 are indeed different versions.</p>
<p>For any version, the main binary package must be called
<code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code>.</p>
<p>The set of currently supported Python 3 versions can be found in
<code class="file docutils literal notranslate"><span class="pre">/usr/share/python3/debian_defaults</span></code>; the supported interface to
this information is through <code class="file docutils literal notranslate"><span class="pre">/usr/bin/py3versions</span></code>.
The set of currently supported Python 2 versions can be found in
<code class="file docutils literal notranslate"><span class="pre">/usr/share/python/debian_defaults</span></code>; the supported interface to
this information is <code class="file docutils literal notranslate"><span class="pre">/usr/bin/pyversions</span></code>.</p>
<p>These files are in Python <code class="docutils literal notranslate"><span class="pre">configparser</span></code> format.
They define (in the <code class="docutils literal notranslate"><span class="pre">DEFAULT</span></code> section) the following options:</p>
<dl class="simple">
<dt><code class="docutils literal notranslate"><span class="pre">default-version</span></code></dt><dd><p>The name of the interpreter for the current default Debian Python.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">supported-versions</span></code></dt><dd><p>The set of interpreter names currently supported and for which
modules should be built and byte-compiled.
This includes <code class="docutils literal notranslate"><span class="pre">default-version</span></code>.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">old-versions</span></code></dt><dd><p>The set of interpreter names which might still be on the system but
for which modules should not be built.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">unsupported-versions</span></code></dt><dd><p>The set of interpreter names which should not be supported at all,
that is modules should not be built or byte-compiled for these.
This includes (is a superset of) <code class="docutils literal notranslate"><span class="pre">old-versions</span></code>.</p>
</dd>
</dl>
<p>Newer versions might also appear in <code class="docutils literal notranslate"><span class="pre">unsupported-versions</span></code> before
being moved to <code class="docutils literal notranslate"><span class="pre">supported-versions</span></code>.</p>
</section>
<section id="main-packages">
<span id="id1"></span><h3><span class="section-number">3.2. </span>Main packages<a class="headerlink" href="#main-packages" title="Permalink to this heading">¶</a></h3>
<p>For every Python version provided in Debian, the binary package
<code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code> shall provide a complete distribution for
<em>deployment</em> of Python scripts and applications.
The package must ensure that the binary <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code>
is provided.</p>
<p>Installation of <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code> shall provide the modules of the
upstream Python distribution with some exceptions.</p>
<p>Excluded are modules that cannot be included for licensing reasons, for
dependency tracking purposes (for example the GPL-licensed <code class="docutils literal notranslate"><span class="pre">gdbm</span></code>
module), or that should not be included for packaging reasons (for
example the <code class="docutils literal notranslate"><span class="pre">tk</span></code> module which depends on Xorg and the <code class="docutils literal notranslate"><span class="pre">venv</span></code> module
which depends on wheels to bootstrap pip).
Modules that would interfere with system package management (for example
<code class="docutils literal notranslate"><span class="pre">ensurepip</span></code>, when used outside virtual environments) are modified to
print a message explaining the problem and recommending alternatives.</p>
<p>Excluded are modules that cannot be included for licensing reasons (for
example the <code class="docutils literal notranslate"><span class="pre">profile</span></code> module), for dependency tracking purposes (for
example the GPL-licensed <code class="docutils literal notranslate"><span class="pre">gdbm</span></code> module), or that should not be
included for packaging reasons (for example the <code class="docutils literal notranslate"><span class="pre">tk</span></code> module which
depends on Xorg).</p>
<p>Some tools and files for the <em>development</em> of Python modules are split
off in a separate binary package <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">-dev</span></code>.</p>
<p>Modules only used for <em>building</em> of Python modules (e.g. <code class="docutils literal notranslate"><span class="pre">distutils</span></code>
and <code class="docutils literal notranslate"><span class="pre">lib2to3</span></code>) are split into separate packages.
The <code class="docutils literal notranslate"><span class="pre">python3-venv</span></code> binary package depends on these.</p>
<p>Documentation will be provided separately as well.</p>
<p>At any time, the <code class="docutils literal notranslate"><span class="pre">python3</span></code> binary package must ensure that
<code class="file docutils literal notranslate"><span class="pre">/usr/bin/python3</span></code> is provided, as a symlink to the current
<code class="samp docutils literal notranslate"><span class="pre">python3.</span><em><span class="pre">Y</span></em></code> executable.
The package must depend on the <code class="samp docutils literal notranslate"><span class="pre">python3.</span><em><span class="pre">Y</span></em></code> package that installs
the executable.</p>
<p>A <code class="docutils literal notranslate"><span class="pre">python3-full</span></code> binary package must ensure that the entire Python
standard library is available, including all modules split into separate
packages (but excluding modules excluded from Debian for licensing
reasons).
This package exists for the convenience of python developers, and must
not be used in dependencies, recommendations and build dependencies by
python module or application packages.</p>
<p>The version of the <code class="docutils literal notranslate"><span class="pre">python3</span></code> package must be greater than or equal to
<code class="samp docutils literal notranslate"><span class="pre">3.</span><em><span class="pre">Y</span></em></code> and lower than <code class="samp docutils literal notranslate"><span class="pre">3.</span><em><span class="pre">Y+1</span></em></code>.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">python</span></code> and <code class="docutils literal notranslate"><span class="pre">python-dbg</span></code> binary packages are to be removed for
Bullseye.
If any Python 2 packages remain in Bullseye, these must depend on
<code class="docutils literal notranslate"><span class="pre">python2</span></code> or <code class="docutils literal notranslate"><span class="pre">python2-dbg</span></code>.
The <code class="docutils literal notranslate"><span class="pre">python2</span></code> package must depend on the <code class="samp docutils literal notranslate"><span class="pre">python2.</span><em><span class="pre">Y</span></em></code> package
that installs the executable <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python2</span></code>.
The version of the <code class="docutils literal notranslate"><span class="pre">python2</span></code> package must be greater than or equal to
<code class="samp docutils literal notranslate"><span class="pre">2.</span><em><span class="pre">Y</span></em></code> and lower than <code class="samp docutils literal notranslate"><span class="pre">2.</span><em><span class="pre">Y+1</span></em></code>.
The <code class="docutils literal notranslate"><span class="pre">python2</span></code> must not provide <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python</span></code>.</p>
<p>For as long as it remains supported, the <code class="docutils literal notranslate"><span class="pre">python</span></code> binary package must
ensure that <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python2</span></code> is provided, as a symlink to the
current <code class="samp docutils literal notranslate"><span class="pre">python2.</span><em><span class="pre">Y</span></em></code> executable.
The package must depend on the <code class="samp docutils literal notranslate"><span class="pre">python2.</span><em><span class="pre">Y</span></em></code> package that installs
the executable.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">python</span></code> binary package must also ensure that
<code class="file docutils literal notranslate"><span class="pre">/usr/bin/python</span></code> is provided, as a symlink to the current
<code class="samp docutils literal notranslate"><span class="pre">python2.</span><em><span class="pre">Y</span></em></code> executable.
See <span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0394/"><strong>PEP 394</strong></a> for details.</p>
<p>The version of the <code class="docutils literal notranslate"><span class="pre">python</span></code> package must be greater than or equal to
<code class="samp docutils literal notranslate"><span class="pre">2.</span><em><span class="pre">Y</span></em></code> and lower than <code class="samp docutils literal notranslate"><span class="pre">2.</span><em><span class="pre">Y+1</span></em></code>.</p>
</section>
<section id="virtual-packages-for-python-version-specific-dependencies">
<h3><span class="section-number">3.3. </span>Virtual packages for Python-version specific dependencies<a class="headerlink" href="#virtual-packages-for-python-version-specific-dependencies" title="Permalink to this heading">¶</a></h3>
<p>The <cite>python3</cite> package provides <cite>python3-supported-min (= {X}.{Y})</cite> and
<cite>python3-supported-max (= {X}.{Y})</cite> virtual packages.
This allows packages to declare dependencies of the form
<code class="samp docutils literal notranslate"><span class="pre">python3-foo</span> <span class="pre">|</span> <span class="pre">python3-supported-min</span> <span class="pre">(>=</span> <span class="pre">3.7)</span></code> or
<code class="samp docutils literal notranslate"><span class="pre">python3-foo</span> <span class="pre">|</span> <span class="pre">python3-supported-max</span> <span class="pre">(<=</span> <span class="pre">3.7)</span></code>, which would
install <cite>python3-foo</cite> if any supported <cite>python3</cite> version requires it.</p>
</section>
<section id="minimal-packages">
<h3><span class="section-number">3.4. </span>Minimal packages<a class="headerlink" href="#minimal-packages" title="Permalink to this heading">¶</a></h3>
<p>For every Python version provided in Debian, the binary package
<code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">-minimal</span></code> might exist and should not be depended
upon by other packages except the Python runtime packages themselves.</p>
</section>
<section id="python-interpreter">
<h3><span class="section-number">3.5. </span>Python Interpreter<a class="headerlink" href="#python-interpreter" title="Permalink to this heading">¶</a></h3>
<section id="interpreter-name">
<span id="id2"></span><h4><span class="section-number">3.5.1. </span>Interpreter Name<a class="headerlink" href="#interpreter-name" title="Permalink to this heading">¶</a></h4>
<p>The different Python major versions require different interpreters
(see <a class="reference internal" href="#main-packages"><span class="std std-ref">Main packages</span></a>).</p>
<p>Python scripts that require the default Python 3 version should specify
<code class="docutils literal notranslate"><span class="pre">python3</span></code> as the interpreter name.</p>
<p>Python scripts that require the default Python 2 version should specify
<code class="docutils literal notranslate"><span class="pre">python2</span></code> as the interpreter name for as long as this remains supported.</p>
<p>Python scripts should not specify <code class="docutils literal notranslate"><span class="pre">python</span></code> as the interpreter name
even if they do not require any particular version of Python as the
script would stop working upon removal of the Python 2 stack.</p>
<p>Python scripts that only work with a specific Python minor version must
explicitly use the versioned interpreter name (<code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code>).</p>
</section>
<section id="interpreter-location">
<span id="id3"></span><h4><span class="section-number">3.5.2. </span>Interpreter Location<a class="headerlink" href="#interpreter-location" title="Permalink to this heading">¶</a></h4>
<p>Python scripts should specify the Debian Python interpreter, to ensure
that the Debian Python installation is used and all dependencies on
additional Python modules are met.</p>
<p>The preferred specification for the Python 3 interpreter is
<code class="file docutils literal notranslate"><span class="pre">/usr/bin/python3</span></code> (or <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python3.</span><em><span class="pre">Y</span></em></code> if it requires
Python <code class="samp docutils literal notranslate"><span class="pre">3.</span><em><span class="pre">Y</span></em></code>).</p>
<p>The preferred specification for the Python 2 interpreter is
<code class="file docutils literal notranslate"><span class="pre">/usr/bin/python2</span></code> (or <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python2.</span><em><span class="pre">Y</span></em></code> if it requires
Python <code class="samp docutils literal notranslate"><span class="pre">2.</span><em><span class="pre">Y</span></em></code>).</p>
<p>Scripts requiring the default Python 2 version must not specify the
interpreter <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python</span></code> as such scripts will fail when the
unversioned interpreter binary <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python</span></code> is removed.</p>
<p>Maintainers should not override the Debian Python interpreter using
<code class="samp docutils literal notranslate"><span class="pre">/usr/bin/env</span> <em><span class="pre">name</span></em></code>.
This is not advisable as it bypasses Debian’s dependency checking and
makes the package vulnerable to incomplete local installations of
Python.</p>
</section>
</section>
<section id="module-path">
<span id="id4"></span><h3><span class="section-number">3.6. </span>Module Path<a class="headerlink" href="#module-path" title="Permalink to this heading">¶</a></h3>
<p>By default, Python modules are searched in the directories listed in the
<span class="target" id="index-1"></span><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONPATH</span></code> environment variable and in the <code class="docutils literal notranslate"><span class="pre">sys.path</span></code> Python
variable.
For all supported Debian releases, <code class="docutils literal notranslate"><span class="pre">sys.path</span></code> does not include a
<code class="file docutils literal notranslate"><span class="pre">/usr/lib/python</span><em><span class="pre">X</span></em><em><span class="pre">Y</span></em><span class="pre">.zip</span></code> entry.</p>
<p>Directories with private Python modules must be absent from the <code class="docutils literal notranslate"><span class="pre">sys.path</span></code>.</p>
<p>Public Python 3 modules must be installed in the system Python 3 modules
directory, <code class="file docutils literal notranslate"><span class="pre">/usr/lib/python3/dist-packages</span></code>.</p>
<p>Public Python 2 modules must be installed in the system Python 2 modules
directory <code class="file docutils literal notranslate"><span class="pre">/usr/lib/python2.</span><em><span class="pre">Y</span></em><span class="pre">/dist-packages</span></code>, where
<code class="samp docutils literal notranslate"><span class="pre">2.</span><em><span class="pre">Y</span></em></code> is the Python 2 version.</p>
<p>A special directory is dedicated to public Python modules installed by
the local administrator, <code class="file docutils literal notranslate"><span class="pre">/usr/local/lib/python3/dist-packages</span></code>
for all Python 3 versions,
<code class="file docutils literal notranslate"><span class="pre">/usr/local/lib/python2.</span><em><span class="pre">Y</span></em><span class="pre">/dist-packages</span></code> for Python 2.</p>
<p>For local installation of Python modules by the system administrator,
special directories are reserved.
The directory <code class="file docutils literal notranslate"><span class="pre">/usr/local/lib/python3/site-packages</span></code> is in the
Python 3 runtime module search path.
The directory <code class="file docutils literal notranslate"><span class="pre">/usr/local/lib/python2.</span><em><span class="pre">Y</span></em><span class="pre">/site-packages</span></code> is in the
Python <code class="samp docutils literal notranslate"><span class="pre">2.</span><em><span class="pre">Y</span></em></code> runtime module search path.</p>
<p>Additional information on appending site-specific paths to the module
search path is available in the official documentation of the <code class="docutils literal notranslate"><span class="pre">site</span></code>
module.</p>
<p>Python modules which work with multiple supported Python 2 versions must
install to version-specific locations, for instance
<code class="file docutils literal notranslate"><span class="pre">/usr/lib/python2.6/dist-packages/foo.py</span></code> and
<code class="file docutils literal notranslate"><span class="pre">/usr/lib/python2.7/dist-packages/foo.py</span></code>.
These should point to a common file.</p>
<p>Architecture-independent public Python 3 modules must be installed to
<code class="file docutils literal notranslate"><span class="pre">/usr/lib/python3/dist-packages</span></code>.</p>
<p>Architecture-independent public Python 2 modules should be installed to
<code class="file docutils literal notranslate"><span class="pre">/usr/lib/python2.7/dist-packages</span></code>.
The historical location for this was <code class="file docutils literal notranslate"><span class="pre">/usr/share/pyshared</span></code>.
Since Python 2.7 is the last Python 2 version and the only supported
version in Wheezy and later releases, a version-specific location is
sufficient.</p>
</section>
<section id="hooks-for-updates-to-installed-runtimes">
<h3><span class="section-number">3.7. </span>Hooks for updates to installed runtimes<a class="headerlink" href="#hooks-for-updates-to-installed-runtimes" title="Permalink to this heading">¶</a></h3>
<p>The <code class="docutils literal notranslate"><span class="pre">python3</span></code> binary package has special hooks to allow other packages
to act upon updates to the installed runtimes.</p>
<p>This mechanism is required to handle changes of the default Python
runtime in some packages and to enable the Python packaging helpers.</p>
<p>There are three supported hook types which come in the form of scripts
which are invoked from the maintainer scripts of the Python runtime
packages when specific installations, removals, or upgrades occur.</p>
<ol class="arabic simple">
<li><p><code class="file docutils literal notranslate"><span class="pre">/usr/share/python3/runtime.d/</span><em><span class="pre">*</span></em><span class="pre">.rtinstall</span></code>:
These are called when a runtime is installed or becomes supported.
The first argument is <code class="docutils literal notranslate"><span class="pre">rtinstall</span></code>, the second argument is the
affected runtime (for example <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code>) and the third
and fourth argument are the old and new version of this packaged
runtime if this runtime was already installed but unsupported.</p></li>
<li><p><code class="file docutils literal notranslate"><span class="pre">/usr/share/python3/runtime.d/</span><em><span class="pre">*</span></em><span class="pre">.rtremove</span></code>:
These are called when a runtime is removed or stops being supported.
The first argument is <code class="docutils literal notranslate"><span class="pre">rtremove</span></code>, and the second argument is the
affected runtime (for example <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code>).</p></li>
<li><p><code class="file docutils literal notranslate"><span class="pre">/usr/share/python3/runtime.d/</span><em><span class="pre">*</span></em><span class="pre">.rtupdate</span></code>:
These are called when the default runtime changes.
The first argument is either <code class="docutils literal notranslate"><span class="pre">pre-rtupdate</span></code>, called before changing
the default runtime, or <code class="docutils literal notranslate"><span class="pre">rtupdate</span></code>, called when changing the
default runtime, or <code class="docutils literal notranslate"><span class="pre">post-rtupdate</span></code>, called immediately afterwards.
The second argument is the old default runtime (for example
<code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code>), and the third argument is the new default
runtime (for example <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Z</span></em></code>).</p></li>
</ol>
</section>
<section id="documentation">
<h3><span class="section-number">3.8. </span>Documentation<a class="headerlink" href="#documentation" title="Permalink to this heading">¶</a></h3>
<p>Python documentation is split out in separate binary packages
<code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">-doc</span></code>.</p>
<p>The binary package <code class="docutils literal notranslate"><span class="pre">python3-doc</span></code> will always provide the documentation
for the default Debian Python 3 version.
The binary package <code class="docutils literal notranslate"><span class="pre">python2-doc</span></code> will always provide the documentation
for the default Debian Python 2 version, for as long as that remains
supported.</p>
<p>TODO: Policy for documentation of third party packages.</p>
</section>
</section>
<span id="document-packaged-modules"></span><section id="packaged-modules">
<h2><span class="section-number">4. </span>Packaged Modules<a class="headerlink" href="#packaged-modules" title="Permalink to this heading">¶</a></h2>
<p>The goal of these policies is to reduce the work necessary for Python
transitions.
Python modules are internally very dependent on a specific Python
version.
However, we want to automate recompiling modules when possible, either
during the upgrade itself (re-compiling bytecode files <code class="file docutils literal notranslate"><em><span class="pre">*</span></em><span class="pre">.pyc</span></code>
and <code class="file docutils literal notranslate"><em><span class="pre">*</span></em><span class="pre">.pyo</span></code>) or shortly thereafter with automated rebuilds (to
handle C extensions).
These policies encourage automated dependency generation and loose
version bounds whenever possible.</p>
<section id="types-of-python-modules">
<h3><span class="section-number">4.1. </span>Types of Python Modules<a class="headerlink" href="#types-of-python-modules" title="Permalink to this heading">¶</a></h3>
<p>There are two kinds of Python modules, “pure” Python modules, and
extension modules.
Pure Python modules are Python source code that generally works across
many versions of Python.
Extensions are C code compiled and linked against a specific version of
the Python runtime, and so can only be used by one version of Python.</p>
<p>Debian Python does not link extensions to <code class="docutils literal notranslate"><span class="pre">libpython</span></code> (as is done in
some operating systems).
Symbols are resolved by <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code> which is not
linked to <code class="docutils literal notranslate"><span class="pre">libpython</span></code>.</p>
<p>Python packages are a way of structuring Python’s module namespace by
using “dotted module names”.
See <a class="reference external" href="https://docs.python.org/3/glossary.html#term-package">Python’s glossary</a> for details on
how packages are defined in Python terms (a package in the Python sense
is unrelated to a Debian package).
Python packages must be packaged into the same directory (as done by
upstream).
Splitting components of a package across directories changes the import
order and may confuse documentation tools and IDEs.</p>
<p>There are two ways to distribute Python modules.
Public modules are installed in a public directory as listed in
<a class="reference internal" href="index.html#module-path"><span class="std std-ref">Module Path</span></a>.
They are accessible to any program.
Private modules are installed in a private directory such as
<code class="file docutils literal notranslate"><span class="pre">/usr/share/</span><em><span class="pre">package-name</span></em></code> or <code class="file docutils literal notranslate"><span class="pre">/usr/lib/</span><em><span class="pre">package-name</span></em></code>.
They are generally only accessible to a specific program or suite of
programs included in the same package.</p>
</section>
<section id="wheels">
<h3><span class="section-number">4.2. </span>Wheels<a class="headerlink" href="#wheels" title="Permalink to this heading">¶</a></h3>
<p><span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0427/"><strong>PEP 427</strong></a> defines a built-package format called “wheels”, which is a
Zip format archive containing Python code and a <code class="file docutils literal notranslate"><em><span class="pre">*</span></em><span class="pre">.dist-info</span></code>
metadata directory, in a single file named with the <code class="docutils literal notranslate"><span class="pre">.whl</span></code> suffix.
As Zip files, wheels containing pure Python can be put on <code class="docutils literal notranslate"><span class="pre">sys.path</span></code>
and modules in the wheel can be imported directly by Python’s <code class="docutils literal notranslate"><span class="pre">import</span></code>
statement.
(Importing extension modules from wheels is not yet supported as of
Python 3.4.)</p>
<p>Except as described below, packages must not build or provide wheels.
They are redundant to the established way of providing Python libraries
to Debian users, take no advantage of distro-based tools, and are less
convenient to use.
E.g. they must be explicitly added to <code class="docutils literal notranslate"><span class="pre">sys.path</span></code>, cannot be easily
grepped, and stack traces through Zip files are more difficult to debug.</p>
<p>A very limited set of wheel packages are available in the archive, but
these support the narrow purpose of enabling the <code class="docutils literal notranslate"><span class="pre">pip</span></code>,
<code class="docutils literal notranslate"><span class="pre">virtualenv</span></code>, and <code class="docutils literal notranslate"><span class="pre">pyvenv</span></code> tools in a Debian policy compliant way.
These packages build their own dependent wheels through the use of the
<code class="docutils literal notranslate"><span class="pre">dirtbike</span></code> “rewheeling” tool, which takes installed Debian packages
and turns them back into wheels.
Only universal wheels (i.e. pure-Python, Python 3 and 2 compatible
packages) are supported, with the exception of wheels of packages that
no longer support Python 2.
Wheels built for these packages are not required to be universal.
Since only the programs that require wheels need build them, only they
may provide <code class="docutils literal notranslate"><span class="pre">-whl</span></code> packages, e.g. <code class="docutils literal notranslate"><span class="pre">python3-pip-whl</span></code>.</p>
<p>When these binary packages are installed, <code class="file docutils literal notranslate"><em><span class="pre">*</span></em><span class="pre">.whl</span></code> files must be
placed in the <code class="file docutils literal notranslate"><span class="pre">/usr/share/python-wheels</span></code> directory.
The location inside a virtual environment will be rooted in the virtual
environment, instead of <code class="file docutils literal notranslate"><span class="pre">/usr</span></code>.</p>
</section>
<section id="module-package-names">
<span id="id1"></span><h3><span class="section-number">4.3. </span>Module Package Names<a class="headerlink" href="#module-package-names" title="Permalink to this heading">¶</a></h3>
<p>Public Python modules must be packaged separately by major Python
version, to preserve run time separation between Python 2 and Python 3.</p>
<p>Public Python 3 modules used by other packages must have their binary
package name prefixed with <code class="docutils literal notranslate"><span class="pre">python3-</span></code>.
It is recommended to use this prefix for all packages with public
modules as they may be used by other packages in the future.</p>
<p>The binary package for module <code class="samp docutils literal notranslate"><em><span class="pre">foo</span></em></code> should preferably be named
<code class="samp docutils literal notranslate"><span class="pre">python3-</span><em><span class="pre">foo</span></em></code>, if the module name allows.
This is not required if the binary package installs multiple modules, in
which case the maintainer shall choose the name of the module which best
represents the package.</p>
<p>For the purposes of package naming, the name that is used for a module
is the name that can be used with <code class="docutils literal notranslate"><span class="pre">import</span></code>, which is not necessarily
the same as the name used in setuptools <code class="docutils literal notranslate"><span class="pre">PKG-INFO</span></code> and <code class="docutils literal notranslate"><span class="pre">.egg-info</span></code>
files and directories.
For example, the module described in <code class="samp docutils literal notranslate"><span class="pre">pyxdg-</span><em><span class="pre">*</span></em><span class="pre">.egg-info</span></code> is used
via <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">xdg</span></code>, so its package name is <code class="docutils literal notranslate"><span class="pre">python3-xdg</span></code> and not
<code class="docutils literal notranslate"><span class="pre">python3-pyxdg</span></code>.</p>
<p>Some modules have names that contain underscores or capital letters,
which are not allowed in Debian package names.
The recommendation is to replace underscores with hyphen/minus and
capital letters with lower-case.
For example, the modules that can be used with <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">distro_info</span></code>
and <code class="docutils literal notranslate"><span class="pre">import</span> <span class="pre">Xlib</span></code> are packaged as <code class="docutils literal notranslate"><span class="pre">python3-distro-info</span></code> and
<code class="docutils literal notranslate"><span class="pre">python3-xlib</span></code> respectively.</p>
<p>For subpackages such as <code class="samp docutils literal notranslate"><em><span class="pre">foo.bar</span></em></code>, the recommendation is to name
the binary package <code class="samp docutils literal notranslate"><span class="pre">python3-</span><em><span class="pre">foo.bar</span></em></code>.</p>
<p>Such a package should support the current Debian Python version,
and more if possible (there are several tools to help implement
this, see <a class="reference internal" href="index.html#packaging-tools"><span class="std std-ref">Packaging Tools</span></a>).
For example, if Python 3.3, 3.4, and 3.5 are supported, the Python
statement</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">foo</span>
</pre></div>
</div>
<p>should import the module when the program interpreter is any of
<code class="file docutils literal notranslate"><span class="pre">/usr/bin/python3.3</span></code>, <code class="file docutils literal notranslate"><span class="pre">/usr/bin/python3.4</span></code>, and
<code class="file docutils literal notranslate"><span class="pre">/usr/bin/python3.5</span></code>.
This requirement also applies to extension modules; binaries for all the
supported Python versions should be included in a single package.</p>
<p>Packages intended for use with Django (<code class="docutils literal notranslate"><span class="pre">python3-django</span></code>) are installed
in the same namespace as other python packages for a variety of reasons.
Many such packages are named <code class="samp docutils literal notranslate"><span class="pre">django_</span><em><span class="pre">name</span></em></code> upstream.
These are then packaged as <code class="samp docutils literal notranslate"><span class="pre">python3-django-</span><em><span class="pre">name</span></em></code>.
This makes it clear that they are intended for use with Django and not
general purpose Python modules.
Debian maintainers are encouraged to work with their upstreams to
support consistent use of this approach.</p>
<p>If the documentation for a module <code class="samp docutils literal notranslate"><em><span class="pre">foo</span></em></code> provided in
<code class="samp docutils literal notranslate"><span class="pre">python3-</span><em><span class="pre">foo</span></em></code> is large enough that a separate binary package for
documentation is desired, then the documentation package should
preferably be named <code class="samp docutils literal notranslate"><span class="pre">python-</span><em><span class="pre">foo</span></em><span class="pre">-doc</span></code> (and in particular, not
<code class="samp docutils literal notranslate"><span class="pre">python3-</span><em><span class="pre">foo</span></em><span class="pre">-doc</span></code>).</p>
</section>
<section id="specifying-supported-versions">
<h3><span class="section-number">4.4. </span>Specifying Supported Versions<a class="headerlink" href="#specifying-supported-versions" title="Permalink to this heading">¶</a></h3>
<p>The <code class="file docutils literal notranslate"><span class="pre">debian/control</span></code> source paragraph may contain optional fields
to specify the versions of Python the package supports.</p>
<p>The optional <code class="docutils literal notranslate"><span class="pre">X-Python3-Version</span></code> field specifies the versions of
Python 3 supported.
When not specified, it defaults to all currently supported Python 3
versions.</p>
<p>Similarly, the optional fields <code class="docutils literal notranslate"><span class="pre">X-Python-Version</span></code> or
<code class="docutils literal notranslate"><span class="pre">XS-Python-Version</span></code> were used to specify the versions of Python 2
supported by the source package.
They are obsolete and must be removed.</p>
<p>These fields are used by some packaging scripts to automatically
generate appropriate Depends and Provides lines.
The format of the field may be one of the following:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">X</span><span class="o">-</span><span class="n">Python3</span><span class="o">-</span><span class="n">Version</span><span class="p">:</span> <span class="o">>=</span> <span class="n">X</span><span class="o">.</span><span class="n">Y</span>
<span class="n">X</span><span class="o">-</span><span class="n">Python3</span><span class="o">-</span><span class="n">Version</span><span class="p">:</span> <span class="o">>=</span> <span class="n">A</span><span class="o">.</span><span class="n">B</span><span class="p">,</span> <span class="o"><<</span> <span class="n">X</span><span class="o">.</span><span class="n">Y</span>
<span class="n">XS</span><span class="o">-</span><span class="n">Python</span><span class="o">-</span><span class="n">Version</span><span class="p">:</span> <span class="n">A</span><span class="o">.</span><span class="n">B</span><span class="p">,</span> <span class="n">X</span><span class="o">.</span><span class="n">Y</span>
</pre></div>
</div>
<p>The keyword <code class="docutils literal notranslate"><span class="pre">all</span></code> is no longer to be used since using version numbers
is clearer than <code class="docutils literal notranslate"><span class="pre">all</span></code> and encodes more information.
The keyword <code class="docutils literal notranslate"><span class="pre">all</span></code> must be ignored for Python 3 versions.</p>
<p>A comma-separated list of multiple individual versions (e.g. <code class="docutils literal notranslate"><span class="pre">3.3,</span> <span class="pre">3.4,</span>
<span class="pre">3.5</span></code>) in <code class="docutils literal notranslate"><span class="pre">XS-Python-Version</span></code> will continue to be supported, but
is not recommended.</p>
<p>The use of multiple individual versions in <code class="docutils literal notranslate"><span class="pre">X-Python-Version</span></code> or
<code class="docutils literal notranslate"><span class="pre">X-Python3-Version</span></code> is not supported for Wheezy and later releases.</p>
<p>The keyword <code class="docutils literal notranslate"><span class="pre">current</span></code> has been deprecated and must not be used.
It must be ignored for Python 3 versions.</p>
<p>The use of <code class="docutils literal notranslate"><span class="pre">XB-Python-Version</span></code> in the binary package paragraphs of
<code class="file docutils literal notranslate"><span class="pre">debian/control</span></code> file has been deprecated and should be removed in
the normal course of package updates.
It never achieved sufficient deployment to support its intended purpose
of managing Python transitions.
This purpose can be adequately accomplished by examining package
dependencies.</p>
</section>
<section id="dependencies">
<h3><span class="section-number">4.5. </span>Dependencies<a class="headerlink" href="#dependencies" title="Permalink to this heading">¶</a></h3>
<p>Any package that installs modules for the default Python version (or
many versions including the default) as described in
<a class="reference internal" href="#module-package-names"><span class="std std-ref">Module Package Names</span></a>, must declare a dependency on the default
Python runtime package.
If it requires other modules to work, the package must declare
dependencies on the corresponding packaged modules.
The package must not declare dependency on any version-specific Python
runtime or module package.</p>
<p>For Python 3, the correct dependencies are <code class="samp docutils literal notranslate"><span class="pre">Depends:</span>
<span class="pre">python3 (>= 3.</span><em><span class="pre">Y</span></em><span class="pre">)</span></code> and any corresponding <code class="samp docutils literal notranslate"><span class="pre">python3-</span><em><span class="pre">foo</span></em></code>
packages.</p>
<p>If any Python 2 packages remain, the correct dependencies are
<code class="samp docutils literal notranslate"><span class="pre">Depends:</span> <span class="pre">python2 (>= 2.</span><em><span class="pre">Y</span></em><span class="pre">)</span></code> and any corresponding
<code class="samp docutils literal notranslate"><span class="pre">python2-</span><em><span class="pre">foo</span></em></code> packages.</p>
<p>Any package that installs Python modules or Python 3 binary extensions
must also declare a maximum version it supports as currently built.
This is accomplished by declaring a maximum version constraint strictly
less than one higher than the current maximum version, i.e.
<code class="samp docutils literal notranslate"><span class="pre">Depends:</span> <span class="pre">python3 (<< </span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">)</span></code>.</p>
</section>
<section id="provides">
<h3><span class="section-number">4.6. </span>Provides<a class="headerlink" href="#provides" title="Permalink to this heading">¶</a></h3>
<p>Binary packages that declare Provides dependencies of the form
<code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">-foo</span></code> were never supported for Python 3.
They should be removed in the normal course of package updates.
Future provision of values for the substitution variable
<code class="docutils literal notranslate"><span class="pre">python:Provides</span></code> is not guaranteed.</p>
</section>
<section id="modules-byte-compilation">
<span id="module-byte-compilation"></span><h3><span class="section-number">4.7. </span>Modules Byte-Compilation<a class="headerlink" href="#modules-byte-compilation" title="Permalink to this heading">¶</a></h3>
<p>If a binary package provides any binary-independent modules
(<code class="file docutils literal notranslate"><em><span class="pre">foo</span></em><span class="pre">.py</span></code> files), the corresponding byte-compiled modules
(<code class="file docutils literal notranslate"><em><span class="pre">foo</span></em><span class="pre">.pyc</span></code> files) and optimized modules (<code class="file docutils literal notranslate"><em><span class="pre">foo</span></em><span class="pre">.pyo</span></code>
files) must not ship in the package.
Instead, they should be generated in the package’s post-install script,
and removed in the package’s pre-remove script.
The package’s <code class="file docutils literal notranslate"><span class="pre">prerm</span></code> has to make sure that both <code class="file docutils literal notranslate"><em><span class="pre">foo</span></em><span class="pre">.pyc</span></code>
and <code class="file docutils literal notranslate"><em><span class="pre">foo</span></em><span class="pre">.pyo</span></code> are removed.</p>
<p>A binary package should only byte-compile the files which belong to the
package.</p>
<p>The file <code class="file docutils literal notranslate"><span class="pre">/etc/python/debian_config</span></code> allows configuration how
modules should be byte-compiled.
The post-install scripts should respect these settings.</p>
<p>Pure Python modules in private installation directories that are
byte-compiled with the default Python version must be forcefully
byte-compiled again when the default Python version changes.</p>
<p>Public Python extensions should be bin-NMUed.</p>
<p>Private Python extensions should be subject to binary NMUs every time
the default interpreter changes, unless the extension is updated through
a <code class="file docutils literal notranslate"><em><span class="pre">*</span></em><span class="pre">.rtupdate</span></code> script.</p>
</section>
</section>
<span id="document-python-programs"></span><section id="python-programs">
<h2><span class="section-number">5. </span>Python Programs<a class="headerlink" href="#python-programs" title="Permalink to this heading">¶</a></h2>
<section id="interpreter-directive-shebang">
<h3><span class="section-number">5.1. </span>Interpreter directive (“Shebang”)<a class="headerlink" href="#interpreter-directive-shebang" title="Permalink to this heading">¶</a></h3>
<p>Executables written for interpretation by Python must use an appropriate
interpreter directive, or “shebang”, as the first line of the program.
This line should be of the form <code class="samp docutils literal notranslate"><span class="pre">#!</span><em><span class="pre">interpreter_location</span></em></code>.
See <a class="reference internal" href="index.html#interpreter-name"><span class="std std-ref">Interpreter Name</span></a> for the interpreter name to use.</p>
<p>As noted in <a class="reference internal" href="index.html#interpreter-location"><span class="std std-ref">Interpreter Location</span></a>, the form <code class="samp docutils literal notranslate"><span class="pre">#!/usr/bin/env</span>
<em><span class="pre">interpreter_name</span></em></code> is deprecated.</p>
</section>
<section id="programs-using-the-default-python">
<h3><span class="section-number">5.2. </span>Programs using the default Python<a class="headerlink" href="#programs-using-the-default-python" title="Permalink to this heading">¶</a></h3>
<p>A package that installs a program that can be run by any version of
Python 3 must declare a dependency on <code class="docutils literal notranslate"><span class="pre">python3</span></code>, with a versioned
dependency if necessary.</p>
<p>A package that installs a program that can be run by any version of
Python 2 must declare a dependency on <code class="docutils literal notranslate"><span class="pre">python2</span></code>, with a versioned
dependency if necessary.</p>
<p>If the program needs the public Python module <code class="docutils literal notranslate"><span class="pre">foo</span></code>, the package must
depend on the binary package that installs the <code class="docutils literal notranslate"><span class="pre">foo</span></code> module.
See <a class="reference internal" href="index.html#module-package-names"><span class="std std-ref">Module Package Names</span></a> for the naming of packages that install
public Python modules.</p>
</section>
<section id="programs-shipping-private-modules">
<h3><span class="section-number">5.3. </span>Programs Shipping Private Modules<a class="headerlink" href="#programs-shipping-private-modules" title="Permalink to this heading">¶</a></h3>
<p>A program that specifies <code class="docutils literal notranslate"><span class="pre">python3</span></code> as its interpreter may require its
own private Python modules.
These modules should be installed in <code class="file docutils literal notranslate"><span class="pre">/usr/share/</span><em><span class="pre">module</span></em></code>, or
<code class="file docutils literal notranslate"><span class="pre">/usr/lib/</span><em><span class="pre">module</span></em></code> if the modules are architecture-dependent
(e.g. extensions).</p>
<p>The rules explained in <a class="reference internal" href="index.html#module-byte-compilation"><span class="std std-ref">Modules Byte-Compilation</span></a> apply to those
private modules: the byte-compiled modules must not be shipped with the
binary package, they should be generated in the package’s post-install
script using the current default Python version, and removed in the
pre-remove script.
Modules should be byte-compiled using the current default Python
version.</p>
<p>Programs that have private compiled extensions must either handle
multiple version support themselves, or declare a tight dependency on
the current Python version (e.g. <code class="docutils literal notranslate"><span class="pre">Depends:</span> <span class="pre">python3 (>= 3.5),</span>
<span class="pre">python3 (<< 3.6)</span></code>.</p>
</section>
<section id="programs-using-a-particular-python-version">
<h3><span class="section-number">5.4. </span>Programs Using a Particular Python Version<a class="headerlink" href="#programs-using-a-particular-python-version" title="Permalink to this heading">¶</a></h3>
<p>A program which requires a specific minor version of Python must specify
the versioned interpreter <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code>.
The package that installs the programs must also specify a dependency on
<code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code> and on any packages that install necessary
modules.</p>
<p>The notes on installation directories and byte-compilation for programs
that support any version of Python also apply to programs supporting
only a single Python version.
Modules to be byte-compiled should use the same Python version as the
package itself.</p>
</section>
</section>
<span id="document-embedded-python"></span><section id="programs-embedding-python">
<h2><span class="section-number">6. </span>Programs Embedding Python<a class="headerlink" href="#programs-embedding-python" title="Permalink to this heading">¶</a></h2>
<section id="building-embedded-programs">
<h3><span class="section-number">6.1. </span>Building Embedded Programs<a class="headerlink" href="#building-embedded-programs" title="Permalink to this heading">¶</a></h3>
<p>Any package that installs a program which embeds a Python interpreter
must declare <code class="docutils literal notranslate"><span class="pre">Build-Depends</span></code> on <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">-dev</span></code>, where
<code class="samp docutils literal notranslate"><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code> is the Python version the program builds against.
It should be the current default Python version unless the program does
not work correctly with this version.</p>
</section>
<section id="embedded-python-dependencies">
<h3><span class="section-number">6.2. </span>Embedded Python Dependencies<a class="headerlink" href="#embedded-python-dependencies" title="Permalink to this heading">¶</a></h3>
<p>Dependencies for programs linking against the shared Python library will
be automatically created by <code class="docutils literal notranslate"><span class="pre">dpkg-shlibdeps</span></code>.
The <code class="samp docutils literal notranslate"><span class="pre">libpython</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">.so.</span><em><span class="pre">Z</span></em></code> library the program is built against
is provided by the <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em></code> package.</p>
</section>
</section>
<span id="document-locally-installed-python"></span><section id="interaction-with-locally-installed-python-versions">
<h2><span class="section-number">7. </span>Interaction with Locally Installed Python Versions<a class="headerlink" href="#interaction-with-locally-installed-python-versions" title="Permalink to this heading">¶</a></h2>
<p>As long as you don’t install other versions of Python in your path,
Debian’s Python versions won’t be affected by a new version.</p>
<p>If you install a different micro version of the version of Python you
have got installed, you will need to be careful to install all the
modules you use for that version of Python too.</p>
</section>
</div>
<div class="toctree-wrapper compound" id="appendix">
<span id="document-build-dependencies"></span><section id="build-dependencies">
<h2><span class="section-number">1. </span>Build Dependencies<a class="headerlink" href="#build-dependencies" title="Permalink to this heading">¶</a></h2>
<p>Build dependencies for Python-dependent packages must be declared for
every Python version that the package is built for.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">python3-all-dev</span></code> should be used when building extensions for any
or all Python 3 versions.
The <code class="docutils literal notranslate"><span class="pre">python-all-dev</span></code> should be used when building extensions for any
or all Python 2 versions.
To build for a specific version or versions, declare <code class="docutils literal notranslate"><span class="pre">Build-Depends</span></code>
on <code class="samp docutils literal notranslate"><span class="pre">python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">-dev</span></code>.</p>
<p>Some applications and pure Python modules may be able to avoid
dependency on the <code class="docutils literal notranslate"><span class="pre">-dev</span></code> packages, and declare <code class="docutils literal notranslate"><span class="pre">Build-Depends</span></code> on
the runtime environment only
(<code class="docutils literal notranslate"><span class="pre">python3</span></code>, <code class="docutils literal notranslate"><span class="pre">python3-all</span></code>, <code class="docutils literal notranslate"><span class="pre">python2</span></code>, <code class="docutils literal notranslate"><span class="pre">python2-all</span></code>).
A package that does not require the <code class="docutils literal notranslate"><span class="pre">-dev</span></code> packages must not declare
<code class="docutils literal notranslate"><span class="pre">Build-Depends</span></code> on them.</p>
<p>Declare <code class="docutils literal notranslate"><span class="pre">Build-Depends</span></code> on at least:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python2</span><span class="mf">.7</span>
<span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python2</span><span class="mf">.6</span> <span class="p">(</span><span class="o">>=</span> <span class="mf">2.6</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python</span> <span class="p">(</span><span class="o">>=</span> <span class="mf">2.6.6</span><span class="o">-</span><span class="mi">9</span><span class="p">)</span>
<span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python</span><span class="o">-</span><span class="nb">all</span>
<span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python2</span><span class="mf">.7</span><span class="o">-</span><span class="n">dev</span>
<span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python3</span><span class="mf">.5</span><span class="o">-</span><span class="n">dev</span> <span class="p">(</span><span class="o">>=</span> <span class="mf">3.5.1</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span>
<span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python</span><span class="o">-</span><span class="n">dev</span> <span class="p">(</span><span class="o">>=</span> <span class="mf">2.6.6</span><span class="o">-</span><span class="mi">9</span><span class="p">)</span>
<span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python</span><span class="o">-</span><span class="nb">all</span><span class="o">-</span><span class="n">dev</span>
<span class="n">Build</span><span class="o">-</span><span class="n">Depends</span><span class="p">:</span> <span class="n">python3</span><span class="o">-</span><span class="nb">all</span><span class="o">-</span><span class="n">dev</span> <span class="p">(</span><span class="o">>=</span> <span class="mf">3.2</span><span class="p">)</span>
</pre></div>
</div>
</section>
<span id="document-packaging-tools"></span><section id="packaging-tools">
<span id="id1"></span><h2><span class="section-number">2. </span>Packaging Tools<a class="headerlink" href="#packaging-tools" title="Permalink to this heading">¶</a></h2>
<p>This section describes the various tools to help package Python programs
and modules for Debian.
Although none of these tools are mandatory, their use is strongly
encouraged, as the above policy has been designed with them in mind (and
vice versa).
This appendix is just an overview.
If you use these tools, you should read their full documentation.</p>
<section id="distutils">
<h3><span class="section-number">2.1. </span>distutils<a class="headerlink" href="#distutils" title="Permalink to this heading">¶</a></h3>
<p>The standard Python <code class="docutils literal notranslate"><span class="pre">distutils</span></code> module has been modified in Debian to
change the default installation directory of public Python modules and
to add a new flag to the <code class="docutils literal notranslate"><span class="pre">install</span></code> command to override the default,
<code class="docutils literal notranslate"><span class="pre">--install-layout=</span></code>.</p>
<p>Public Python modules installed with a modified distutils default to
<code class="file docutils literal notranslate"><span class="pre">/usr/local/lib/python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">/dist-packages</span></code> for Python 2.6 and
later.
This directory is seen by the system-provided Python 2.6.</p>
<p>When using a local Python installation, the default is
<code class="file docutils literal notranslate"><span class="pre">/usr/local/lib/python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">/site-packages</span></code> which is only seen by
the local Python installation.</p>
<p>Using the <code class="docutils literal notranslate"><span class="pre">--install-layout=deb</span></code> flag to the <code class="docutils literal notranslate"><span class="pre">install</span></code> command of
<code class="file docutils literal notranslate"><span class="pre">setup.py</span></code> with a system-provided Python 2.6 or later versions,
Python modules will be installed to
<code class="file docutils literal notranslate"><span class="pre">/usr/lib/python</span><em><span class="pre">X</span></em><span class="pre">.</span><em><span class="pre">Y</span></em><span class="pre">/dist-packages</span></code> which is only seen by the
system-provided Python, not by a local installation.</p>
</section>
<section id="setuptools">
<h3><span class="section-number">2.2. </span>setuptools<a class="headerlink" href="#setuptools" title="Permalink to this heading">¶</a></h3>
<p>The related Python <code class="docutils literal notranslate"><span class="pre">setuptools</span></code> module has been modified in Debian
along the same lines as <code class="docutils literal notranslate"><span class="pre">distutils</span></code>.</p>
<p>Upstream focus on developments and improvements for Python packaging
tools has largely shifted away from <code class="docutils literal notranslate"><span class="pre">distutils</span></code> and to <code class="docutils literal notranslate"><span class="pre">setuptools</span></code>.
They offer a similar API and at some point in the future, <code class="docutils literal notranslate"><span class="pre">setuptools</span></code>
may fully replace <code class="docutils literal notranslate"><span class="pre">distutils</span></code> in Debian package builds.</p>
</section>
<section id="dh-python">
<h3><span class="section-number">2.3. </span>dh-python<a class="headerlink" href="#dh-python" title="Permalink to this heading">¶</a></h3>
<p><code class="docutils literal notranslate"><span class="pre">dh-python</span></code> provides extensions for <code class="docutils literal notranslate"><span class="pre">debhelper</span></code> to make it easier to
package Python modules and extensions.
They calculate Python dependencies, add maintainer scripts to byte
compile files, etc.
Their use is not mandatory, but they are recommended by the Debian
Python maintainers.
See <a class="reference external" href="https://manpages.debian.org/dh_python3">man dh_python3</a> for
details.</p>
</section>
<section id="pybuild">
<h3><span class="section-number">2.4. </span>pybuild<a class="headerlink" href="#pybuild" title="Permalink to this heading">¶</a></h3>
<p>Pybuild is a Debian Python specific build system that invokes various
build systems for requested Python versions in order to build modules
and extensions.
It supports automatically building for multiple Python versions.</p>
</section>
<section id="cdbs">
<h3><span class="section-number">2.5. </span>CDBS<a class="headerlink" href="#cdbs" title="Permalink to this heading">¶</a></h3>
<p>The CDBS <code class="file docutils literal notranslate"><span class="pre">python-distutils.mk</span></code> class helps packaging of distutils
based Python packages.</p>
</section>
<section id="python-support-removed">
<h3><span class="section-number">2.6. </span>python-support (removed)<a class="headerlink" href="#python-support-removed" title="Permalink to this heading">¶</a></h3>
<p><code class="docutils literal notranslate"><span class="pre">python-support</span></code> provided another way to manage Python modules.
It has been removed from Debian Stretch and later releases.</p>
</section>
<section id="python-central-removed">
<h3><span class="section-number">2.7. </span>python-central (removed)<a class="headerlink" href="#python-central-removed" title="Permalink to this heading">¶</a></h3>
<p><code class="docutils literal notranslate"><span class="pre">python-central</span></code> provided another way to manage Python modules.
It has been removed from Debian Jessie and later releases.</p>
</section>
</section>
<span id="document-upgrade-procedure"></span><section id="upgrade-procedure">
<h2><span class="section-number">3. </span>Upgrade Procedure<a class="headerlink" href="#upgrade-procedure" title="Permalink to this heading">¶</a></h2>
<p>This section describes the procedure for the upgrade when the
default Python version is changed in the Debian <code class="docutils literal notranslate"><span class="pre">unstable</span></code> release,
requiring recompilation of many Python-related packages.</p>
<ol class="arabic simple">
<li><p>Selected pre-releases and release candidates of new Python versions
are uploaded to Debian <code class="docutils literal notranslate"><span class="pre">experimental</span></code> to support pre-transition
work and testing.</p></li>
<li><p>Application and module maintainers make sourceful changes where
needed to prepare for the new Python version when needed.</p></li>
<li><p>Have a long and heated discussion.</p></li>
<li><p>The Debian Python maintainer and module/application maintainers
discuss the readiness for a new default Debian Python version and
associated packaging/policy changes.
Once there is some consensus, the Python maintainer announces the
upgrade and uploads to <code class="docutils literal notranslate"><span class="pre">unstable</span></code>.</p></li>
<li><p>Upload of the Python core meta-packages <code class="docutils literal notranslate"><span class="pre">python3</span></code>,
<code class="docutils literal notranslate"><span class="pre">python3-dev</span></code>, <code class="docutils literal notranslate"><span class="pre">python3-doc</span></code> and several
<code class="samp docutils literal notranslate"><span class="pre">python3-</span><em><span class="pre">module</span></em></code>, depending on the new <code class="samp docutils literal notranslate"><span class="pre">python3.</span><em><span class="pre">Y</span></em></code>,
<code class="samp docutils literal notranslate"><span class="pre">python3.</span><em><span class="pre">Y</span></em><span class="pre">-dev</span></code> and so on.</p></li>
<li><p>The Debian release team schedules rebuilds for packages that may
need it.
Packages that require additional manual work get updated and
uploaded.</p></li>
</ol>
<p>The necessary package builds are typically done in three phases in order
to keep transitions as smooth as possible.
For Python 3, there is no general need to update architecture all
packages for a new Python 3 version. Only architecture any packages need
to be rebuilt.</p>
<ol class="arabic simple">
<li><p>The new Python 3 version is added to supported versions and packages
that support multiple Python 3 versions are binNMUed.
They now support both the new and older Python 3 versions.
This requires transition assistance from the release team in the form
of a transition tracker and binNMU scheduling, but is not a
transition that can cause entanglements with other transitions in
Debian.</p></li>
<li><p>Once the default Python 3 version is changed, binNMUs are done for
packages that only support one Python 3 version.
Some transient uninstallability is unavoidable.
This is a transition that can entangle other transitions in Debian
and requires more careful coordination with the release team.</p></li>
<li><p>After the old Python 3 version is dropped from supported versions
then packages with multi-version support are binNMUed again to remove
support for the old Python 3 version.
This is not a true transition and only needs a tracker and binNMU
scheduling.</p></li>
</ol>
</section>
<span id="document-this-document"></span><section id="this-document">
<h2><span class="section-number">4. </span>This document<a class="headerlink" href="#this-document" title="Permalink to this heading">¶</a></h2>
<p>Source of this document is <code class="file docutils literal notranslate"><span class="pre">policy/</span></code> in git repository
<a class="reference external" href="https://salsa.debian.org/cpython-team/python3-defaults">python3-defaults</a>.</p>
<p>Propose changes to this policy on the <a class="reference external" href="https://lists.debian.org/debian-python/">debian-python mailing list</a> for review.</p>
</section>
</div>
</section>
<section id="indices-and-tables">
<h1>Indices and tables<a class="headerlink" href="#indices-and-tables" title="Permalink to this heading">¶</a></h1>
<ul class="simple">
<li><p><a class="reference internal" href="genindex.html"><span class="std std-ref">Index</span></a></p></li>
<li><p><a class="reference internal" href="py-modindex.html"><span class="std std-ref">Module Index</span></a></p></li>
<li><p><a class="reference internal" href="search.html"><span class="std std-ref">Search Page</span></a></p></li>
</ul>
</section>
<div class="clearer"></div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<div>
<h3><a href="#">Table of Contents</a></h3>
<ul>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-copyright">1. Copyright</a></li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-python3">2. Completing the move to Python 3</a><ul>
<li class="toctree-l2"><a class="reference internal" href="index.html#removal-of-the-unversioned-packages">2.1. Removal of the unversioned packages</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#unversioned-python-commands">2.2. Unversioned python commands</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-interpreter">3. Python Packaging</a><ul>
<li class="toctree-l2"><a class="reference internal" href="index.html#versions">3.1. Versions</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#main-packages">3.2. Main packages</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#virtual-packages-for-python-version-specific-dependencies">3.3. Virtual packages for Python-version specific dependencies</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#minimal-packages">3.4. Minimal packages</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#python-interpreter">3.5. Python Interpreter</a><ul>
<li class="toctree-l3"><a class="reference internal" href="index.html#interpreter-name">3.5.1. Interpreter Name</a></li>
<li class="toctree-l3"><a class="reference internal" href="index.html#interpreter-location">3.5.2. Interpreter Location</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="index.html#module-path">3.6. Module Path</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#hooks-for-updates-to-installed-runtimes">3.7. Hooks for updates to installed runtimes</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#documentation">3.8. Documentation</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-packaged-modules">4. Packaged Modules</a><ul>
<li class="toctree-l2"><a class="reference internal" href="index.html#types-of-python-modules">4.1. Types of Python Modules</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#wheels">4.2. Wheels</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#module-package-names">4.3. Module Package Names</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#specifying-supported-versions">4.4. Specifying Supported Versions</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#dependencies">4.5. Dependencies</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#provides">4.6. Provides</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#modules-byte-compilation">4.7. Modules Byte-Compilation</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-python-programs">5. Python Programs</a><ul>
<li class="toctree-l2"><a class="reference internal" href="index.html#interpreter-directive-shebang">5.1. Interpreter directive (“Shebang”)</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#programs-using-the-default-python">5.2. Programs using the default Python</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#programs-shipping-private-modules">5.3. Programs Shipping Private Modules</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#programs-using-a-particular-python-version">5.4. Programs Using a Particular Python Version</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-embedded-python">6. Programs Embedding Python</a><ul>
<li class="toctree-l2"><a class="reference internal" href="index.html#building-embedded-programs">6.1. Building Embedded Programs</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#embedded-python-dependencies">6.2. Embedded Python Dependencies</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-locally-installed-python">7. Interaction with Locally Installed Python Versions</a></li>
</ul>
<p class="caption" role="heading"><span class="caption-text">Appendix</span></p>
<ul>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-build-dependencies">1. Build Dependencies</a></li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-packaging-tools">2. Packaging Tools</a><ul>
<li class="toctree-l2"><a class="reference internal" href="index.html#distutils">2.1. distutils</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#setuptools">2.2. setuptools</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#dh-python">2.3. dh-python</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#pybuild">2.4. pybuild</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#cdbs">2.5. CDBS</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#python-support-removed">2.6. python-support (removed)</a></li>
<li class="toctree-l2"><a class="reference internal" href="index.html#python-central-removed">2.7. python-central (removed)</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-upgrade-procedure">3. Upgrade Procedure</a></li>
<li class="toctree-l1"><a class="reference internal" href="index.html#document-this-document">4. This document</a></li>
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