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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 2. Python Packaging</title><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="home" href="index.html" title="Debian Python Policy" /><link rel="up" href="index.html" title="Debian Python Policy" /><link rel="prev" href="python3.html" title="Chapter 1. On the move to Python 3" /><link rel="next" href="module_packages.html" title="Chapter 3. Packaged Modules" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 2. Python Packaging</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="python3.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="module_packages.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a id="python"></a>Chapter 2. Python Packaging</h1></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><a href="python.html#versions">2.1. Versions</a></span></dt><dt><span class="section"><a href="python.html#base">2.2. Main packages</a></span></dt><dt><span class="section"><a href="python.html#minimal">2.3. Minimal packages</a></span></dt><dt><span class="section"><a href="python.html#interpreter">2.4. Python Interpreter</a></span></dt><dd><dl><dt><span class="section"><a href="python.html#interpreter_name">2.4.1. Interpreter Name</a></span></dt><dt><span class="section"><a href="python.html#interpreter_loc">2.4.2. Interpreter Location</a></span></dt></dl></dd><dt><span class="section"><a href="python.html#paths">2.5. Module Path</a></span></dt><dt><span class="section"><a href="python.html#runtimes_hooks">2.6. Hooks for updates to installed runtimes</a></span></dt><dt><span class="section"><a href="python.html#docs">2.7. Documentation</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="versions"></a>2.1. Versions</h2></div></div></div><p>
	  At any given time, the binary package <code class="literal">python3</code>
	  will represent the current default Debian Python 3 version; the
	  binary package <code class="literal">python</code> will represent the
	  current default Debian Python 2 version. 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="literal">dh-python</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="literal">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em></code>.
	</p><p>
	  The set of currently supported Python 3 versions can be found
	  in <code class="filename">/usr/share/python3/debian_defaults</code>; the supported
	  interface to this information is
	  through <code class="filename">/usr/bin/py3versions</code>.
	  The set of currently supported Python 2 versions can be found in
	  <code class="filename">/usr/share/python/debian_defaults</code>; the supported
	  interface to this information is <code class="filename">/usr/bin/pyversions</code>.
	</p><p>
	  These files are in Python <code class="literal">configparser</code> format. They
	  define (in the <code class="literal">DEFAULT</code> section) the following options:
	  </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">default-version</code>: The name of the interpreter for
	      the current default Debian Python.</p></li><li class="listitem"><p><code class="literal">supported-versions</code>: The set of interpreter names
	      currently supported and for which modules should be built and
	      byte-compiled. This includes <code class="literal">default-version</code>.</p></li><li class="listitem"><p><code class="literal">old-versions</code>: The set of interpreter names which
	      might still be on the system but for which modules should not
	      be built.</p></li><li class="listitem"><p><code class="literal">unsupported-versions</code>: 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="literal">old-versions</code>.</p></li></ul></div><p>
	</p><p>
	  Newer versions might also appear in <code class="literal">unsupported-versions</code>
	  before being moved to <code class="literal">supported-versions</code>.
	</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="base"></a>2.2. Main packages</h2></div></div></div><p>
	  For every Python version provided in Debian, the binary
	  package <code class="literal">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em></code> shall
	  provide a complete distribution for <span class="emphasis"><em>deployment</em></span> of Python
	  scripts and applications. The package must ensure that the binary
	  <code class="filename">/usr/bin/python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em></code> is provided.
	</p><p>
	  Installation of <code class="literal">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></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 example the <code class="literal">profile</code> module), for dependency tracking
	  purposes (for example the GPL-licensed <code class="literal">gdbm</code> module), or
	  that should not be included for packaging reasons (for example
	  the <code class="literal">tk</code> module which depends on Xorg).
	</p><p>
	  Some tools and files for the <span class="emphasis"><em>development</em></span> of Python
	  modules are split off in a separate binary package
	  <code class="literal">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em>-dev</code>.
	</p><p>
	  Documentation will be provided separately as well.
	</p><p>
	  At any time, the <code class="literal">python3</code> binary package must
	  ensure that <code class="filename">/usr/bin/python3</code> is provided, as a
	  symlink to the current <code class="filename">python3.<em class="replaceable"><code>Y</code></em></code>
	  executable. The package must depend on
	  the <code class="literal">python3.<em class="replaceable"><code>Y</code></em></code> package that installs
	  the executable.
	</p><p>
	  The version of the <code class="literal">python3</code> package must be
	  greater than or equal to 3.<em class="replaceable"><code>Y</code></em> and lower than
	  3.<em class="replaceable"><code>Y+1</code></em>.
	</p><p>
	  At any time, the <code class="literal">python</code> binary package must
	  ensure that <code class="filename">/usr/bin/python2</code> is provided, as a
	  symlink to the current <code class="filename">python2.<em class="replaceable"><code>Y</code></em></code>
	  executable. The package must depend on
	  the <code class="literal">python2.<em class="replaceable"><code>Y</code></em></code> package that installs
	  the executable.
	</p><p>
	  The version of the <code class="literal">python</code> package must be
	  greater than or equal to 2.<em class="replaceable"><code>Y</code></em> and lower than
	  2.<em class="replaceable"><code>Y+1</code></em>.
	</p><p>
	  The <code class="literal">python</code> binary package must also ensure
	  that <code class="filename">/usr/bin/python</code> is provided, as a symlink to the
	  current <code class="filename">python2.<em class="replaceable"><code>Y</code></em></code> executable. See
	  <a class="ulink" href="https://www.python.org/dev/peps/pep-0394/" target="_blank">PEP 394</a> for details.
	</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="minimal"></a>2.3. Minimal packages</h2></div></div></div><p>
	  For every Python version provided in Debian, the binary package
	  <code class="literal">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em>-minimal</code> might
	  exist and should not be depended upon by other packages except the
	  Python runtime packages themselves.
	</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="interpreter"></a>2.4. Python Interpreter</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="section"><a href="python.html#interpreter_name">2.4.1. Interpreter Name</a></span></dt><dt><span class="section"><a href="python.html#interpreter_loc">2.4.2. Interpreter Location</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="interpreter_name"></a>2.4.1. Interpreter Name</h3></div></div></div><p>
	    The different Python major versions require different
	    interpreters (see <a class="xref" href="python.html#base" title="2.2. Main packages">Section 2.2, “Main packages”</a>).
	  </p><p>
	    Python scripts that require the default Python 3 version should
	    specify <code class="filename">python3</code> as the interpreter name.
	  </p><p>
	    Python scripts that require the default Python 2 version should
	    specify <code class="filename">python2</code> as the interpreter name.
	  </p><p>
	    Python scripts may specify <code class="filename">python</code> as the
	    interpreter name only if they do not require any particular
	    version of Python. (Note: this means any python2 version)
	  </p><p>
	    Python scripts that only work with a specific Python minor
	    version must explicitly use the versioned interpreter name
	    (<code class="filename">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em></code>).
	  </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="interpreter_loc"></a>2.4.2. Interpreter Location</h3></div></div></div><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="filename">/usr/bin/python3</code> (or
	    <code class="filename">/usr/bin/python3.<em class="replaceable"><code>Y</code></em></code> if it requires Python
	    3.<em class="replaceable"><code>Y</code></em>).
	  </p><p>
	    The preferred specification for the Python 2 interpreter is
	    <code class="filename">/usr/bin/python2</code> (or
	    <code class="filename">/usr/bin/python2.<em class="replaceable"><code>Y</code></em></code> if it requires Python
	    2.<em class="replaceable"><code>Y</code></em>).
	  </p><p>
	    Scripts requiring the default Python 2 version may instead
	    specify the interpreter <code class="filename">/usr/bin/python</code>.
	  </p><p>
	    Maintainers should not override the Debian Python interpreter
	    using <code class="filename">/usr/bin/env <em class="replaceable"><code>name</code></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></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="paths"></a>2.5. Module Path</h2></div></div></div><p>
	  By default, Python modules are searched in the directories listed
	  in the <code class="literal">PYTHONPATH</code> environment variable and in
	  the <code class="literal">sys.path</code> Python variable. For all supported Debian
	  releases, <code class="literal">sys.path</code> does not include
	  a <code class="filename">/usr/lib/python<em class="replaceable"><code>X</code></em><em class="replaceable"><code>Y</code></em>.zip</code> entry.
	</p><p>
	  Directories with private Python modules must be absent from the
	  <code class="literal">sys.path</code>.
	</p><p>
	  Public Python 3 modules must be installed in the system Python 3
	  modules directory, <code class="filename">/usr/lib/python3/dist-packages</code>.
	</p><p>
	  Public Python 2 modules must be installed in the system Python 2
	  modules directory
	  <code class="filename">/usr/lib/python2.<em class="replaceable"><code>Y</code></em>/dist-packages</code>, where
	  2.<em class="replaceable"><code>Y</code></em> is the Python 2 version.
	</p><p>
	  A special directory is dedicated to public Python modules
	  installed by the local administrator,
	  <code class="filename">/usr/lib/python3/dist-packages</code> for all Python 3 versions,
	  <code class="filename">/usr/local/lib/python2.<em class="replaceable"><code>Y</code></em>/dist-packages</code> for
	  Python 2.
	</p><p>
	  For local installation of Python modules by the system
	  administrator, special directories are reserved. The
	  directory <code class="filename">/usr/local/lib/python3/site-packages</code> is in
	  the Python 3 runtime module search path. The
	  directory <code class="filename">/usr/local/lib/python2.<em class="replaceable"><code>Y</code></em>/site-packages</code>
	  is in the Python 2.<em class="replaceable"><code>Y</code></em> 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="literal">site</code> module.
	</p><p>
	  Python modules which work with multiple supported Python 2
	  versions must install to version-specific locations, for instance
	  <code class="filename">/usr/lib/python2.6/dist-packages/foo.py</code> and
	  <code class="filename">/usr/lib/python2.7/dist-packages/foo.py</code>. These should
	  point to a common file.
	</p><p>
	  Architecture-independent public Python 3 modules must be installed
	  to <code class="filename">/usr/lib/python3/dist-packages</code>.
	</p><p>
	  Architecture-independent public Python 2 modules should be
	  installed to <code class="filename">/usr/lib/python2.7/dist-packages</code>. The
	  historical location for this was <code class="filename">/usr/share/pyshared</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></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="runtimes_hooks"></a>2.6. Hooks for updates to installed runtimes</h2></div></div></div><p>
	  The <code class="literal">python</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><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
	      <code class="filename">/usr/share/python3/runtime.d/*.rtinstall</code>,
	      <code class="filename">/usr/share/python/runtime.d/*.rtinstall</code>: These
	      are called when a runtime is installed or becomes supported.
	      The first argument is <code class="literal">rtinstall</code>, the second argument
	      is the affected runtime (for
	      example <code class="filename">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></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 class="listitem"><p>
	      <code class="filename">/usr/share/python3/runtime.d/*.rtremove</code>,
	      <code class="filename">/usr/share/python/runtime.d/*.rtremove</code>: These are
	      called when a runtime is removed or stops being supported. The
	      first argument is <code class="literal">rtremove</code>, and the second argument
	      is the affected runtime (for
	      example <code class="filename">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em></code>).
	    </p></li><li class="listitem"><p>
	      <code class="filename">/usr/share/python3/runtime.d/*.rtupdate</code>,
	      <code class="filename">/usr/share/python/runtime.d/*.rtupdate</code>: These are
	      called when the default runtime changes. The first argument is
	      either <code class="literal">pre-rtupdate</code>, called before changing the
	      default runtime, or <code class="literal">rtupdate</code>, called when changing
	      the default runtime, or <code class="literal">post-rtupdate</code>, called
	      immediately afterwards. The second argument is the old default
	      runtime (for
	      example <code class="filename">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em></code>), and the
	      third argument is the new default runtime (for example
	      <code class="filename">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Z</code></em></code>).
	    </p></li></ol></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="docs"></a>2.7. Documentation</h2></div></div></div><p>
	  Python documentation is split out in separate binary packages
	  <code class="literal">python<em class="replaceable"><code>X</code></em>.<em class="replaceable"><code>Y</code></em>-doc</code>.
	</p><p>
	  The binary package <code class="literal">python3-doc</code> will always
	  provide the documentation for the default Debian Python 3 version.
	  The binary package <code class="literal">python-doc</code> will always
	  provide the documentation for the default Debian Python 2 version.
	</p><p>
	  TODO: Policy for documentation of third party packages.
	</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="python3.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="module_packages.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 1. On the move to Python 3 </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 3. Packaged Modules</td></tr></table></div></body></html>