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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. Completing 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, 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="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>
The <code class="literal">python</code> and <code class="literal">python-dbg</code>
binary packages are to be removed for Bullseye. If any Python 2
packages remain in Bullseye, these must depend on
<code class="literal">python2</code> or <code class="literal">python2-dbg</code>.
The <code class="literal">python2</code> package must depend on the
<code class="literal">python2.<em class="replaceable"><code>Y</code></em></code>
package that installs the executable <code class="filename">/usr/bin/python2</code>.
The version of the <code class="literal">python2</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>.
The <code class="literal">python2</code> must not provide <code class="filename">/usr/bin/python</code>.
</p><p>
For as long as it remains supported, 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 <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><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></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
for as long as this remains supported.
</p><p>
Python scripts should not specify <code class="filename">python</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="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 must not
specify the interpreter <code class="filename">/usr/bin/python</code>
as such scripts will fail when the unversioned interpreter
binary <code class="filename">/usr/bin/python</code> is removed.
</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">python3</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>: 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>: 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>: 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">python2-doc</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></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. Completing 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>
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