<!doctype debiandoc system>

<debiandoc>
  <book>
    <titlepag>
      <title>Debian Python Policy</title>
      <author>
	<name>Neil Schemenauer</name>
	<email>nas@debian.org</email>
      </author>
      <author>
	<name>Matthias Klose</name>
	<email>doko@debian.org</email>
      </author>
      <author>
	<name>Gregor Hoffleit</name>
	<email>flight@debian.org</email>
      </author>
      <version>version 0.3.7</version>

      <abstract>
	This document describes the packaging of Python within the
	Debian GNU/Linux distribution and the policy requirements for
	packaged Python programs and modules.
      </abstract>

      <copyright>
	<copyrightsummary>
	  Copyright &copy; 1999, 2001 Software in the Public Interest
	</copyrightsummary>
	<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 is available as
	  <tt>/usr/share/common-licences/GPL</tt> in the Debian GNU/Linux
	  distribution or on the World Wide Web at
	  <url id="http://www.gnu.org/copyleft/gpl.html"
	  name="The GNU Public Licence">.
	</p>
	<p>
	  You can also obtain it by writing to the
	  Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	  Boston, MA 02111-1307, USA.
	</p>
      </copyright>
    </titlepag>

    <toc detail="sect1">

    <chapt id="python">
      <heading>Python Packaging</heading>
      <sect id="versions">
	<heading>Versions</heading>
	<p>
	  At any given time, the package <package>python</package> will
	  represent the current default Debian Python version.
	</p>
	<p>
	  The default Debian Python version should alway be the latest stable
	  upstream release that can be integrated in the distribution.
	</p>
	<p>
	  Apart from the default version, legacy versions of Python
	  may be included as well in the distribution, as long as they
	  are needed by other packages, or as long as it seems
	  reasonable to provide them.  (Note: For the scope of this
	  document, Python versions are synonymous to feature
	  releases, i.e. Python 2.0 and 2.0.1 are subminor versions of
	  the same Python version 2.0, but Python 2.1 and 2.2 are
	  indeed different versions.)
	</p>
	<p>
	  For any version, the main package must be called
	  <package>python<var>X</var>.<var>Y</var></package>. Names of
	  related packages must include the
	  <package>python<var>X</var>.<var>Y</var></package> part.
	</p>

      </sect>

      <sect id="base">
	<heading>Main package</heading>
	<p>
	  For every Python version provided in the distribution, the
	  package <package>python<var>X</var>.<var>Y</var></package>
	  shall comprise a complete distribution for
	  <em>deployment</em> of Python scripts and applications. The
	  package includes the binary
	  <file>/usr/bin/python<var>X</var>.<var>Y</var></file> and
	  all modules of the upstream Python distribution.
	</p>
	<p>
	  Excluded are any modules that depend on
	  non-<em>required</em> packages, they will be provided in
	  separate packages.  Some tools and files for the
	  <em>development</em> of Python modules are split off in a
	  separate package
	  <package>python<var>X</var>.<var>Y</var>-dev</package>.
	  Documentation will be provided separately as well.
	</p>

	<p>
	  At any time, exactly one package must contain a binary
	  <file>/usr/bin/python</file>. That package must either be
	  <package>python</package> or a dependency of that package.
	</p>
      </sect>


      <sect id="interpreter">
        <heading>Python Interpreter</heading>
        <sect1 id="interpreter_name">
          <heading>Interpreter Name</heading>
          <p>
	    Python scripts depending on the default Python version (see <ref
	    id="base">) or not depending on a specific Python version should
	    use <file>python</file> (unversioned) as the interpreter name.
	    </p>
          <p>
	    Python scripts that only work with a specific Python version must
	    explicitely use the versioned interpreter name
	    (<file>python<var>X</var>.<var>Y</var></file>).
          </p>
        </sect1>
        <sect1 id="interpreter_loc">
          <heading>Interpreter Location</heading>
          <p>
	    The preferred specification for the Python interpreter is
            <file>/usr/bin/python</file> or
            <file>/usr/bin/python<var>X</var>.<var>Y</var></file>.
          </p>
          <p>
	    If a maintainer would like to provide the user with the
	    possibility to override the Debian Python interpreter, he
	    may want to use <file>/usr/bin/env python</file> or
	    <file>/usr/bin/env pythonX.Y</file>.
	  </p>
        </sect1>
      </sect>



      <sect id="paths">
	<heading>Module Path</heading>
	<p>
	  The module search path for Debian has been amended to
	  include a directory tree in /usr/local at the beginning of
	  the path. By default, sys.path is searched in the following
	  order:
	  <example>
/usr/local/lib/python<var>X</var>.<var>Y</var>/site-packages
/usr/local/lib/site-python
/usr/lib/python<var>X</var>.<var>Y</var>/site-packages
/usr/lib/site-python
	  </example>
	</p>
	<p>
	  Note that the use of the site-python directories in Python is
	  depreciated. The directories might be dropped from the path in a
	  future version.
	</p>

	<p>
	  TODO: What about
	  <file>/usr/share/python<var>X</var>.<var>Y</var></file> ?
	</p>

      </sect>

      <sect id="docs">
	<heading>Documentation</heading>
	<p>
	  Python documentation is split out in separate packages
	  <package>python<var>X</var>.<var>Y</var>-doc</package>. The package
	  <package>python-doc</package> will always provide the documentation
	  for the default Debian Python version.
	</p>
	<p>
	  TODO: Policy for documentation of third party packages.
	</p>
      </sect>
    </chapt>

    <chapt id="module_packages">
      <heading>Packaged Modules</heading>

      <sect>
        <heading>Rationale: A different view</heading>
        <p>
	  A package with a name
	  <package>python-<var>foo</var></package> will always
	  provide the module <var>foo</var> for the default Debian
	  Python version of the distribution. I.e. the package will
	  extend the function of <file>/usr/bin/python</file> (which
	  is installed by the package <package>python</package>).
	</p>
	<p>
	  The system of dependencies of the default packages is robust
	  against upgrades, but introduces a strong dependency:
	  I.e. an upgrade of the <package>python</package> package
	  will be hold back as long as there are still default modules
	  packages left over on the system that can't be upgraded to
	  the new version.
	</p>
	<p>
	  The versioned packages (legacy versions) ensure that an
	  upgrade to a new default version can take place before
	  without upgrading *all* packages with dependencies on
	  Python.
	</p>
      </sect>

      <sect id="variants">
	<heading>Packaging Variants</heading>
	<p>
	  There is more than one way to package a Python module:
	  <enumlist>
	    <item>
	      <p>
		Support only the default Python version.
	      </p>
	    </item>
	    <item>
	      <p>
		Support a particular version, or some but not all versions of
		Python available in Debian.
	      </p>
	    </item>
	    <item>
	      <p>
		Support all/most versions of python, including the default.
		Works only for architecture independant python modules.
	      </p>
	    </item>
	  </enumlist>
	</p>

	<sect1 id="default_version">
	  <heading>Support Only The Default Version</heading>
	  <p>
	    Name your package
	    <package>python-<var>foo</var></package>.  This kind of
	    package is called a <em>default module package</em>.
	    Install your modules into
	    <file>/usr/lib/python<var>X</var>.<var>Y</var>/site-packages/</file>.
	    Make your package dependency look like
	    <example>
Depends: python (>= X.Y), python (<< X.Y+1)
	    </example>
	    Note that this kind of packaging means that your package will
	    trigger a conflict when the default Debian Python version in the
	    distribution is changed, and that you will have to provide a new
	    version as soon as possible, since the package will block the
	    upgrade of <package>python</package>.
	  </p>
	  <p>
	    You should not make a default, unversioned module package
	    <package>python-<var>foo</var></package> depend on the
	    versioned Python package
	    <package>python<var>X</var>.<var>Y</var></package>!
	  </p>
	  <p>
	    The source package must declare
	    <example>
Build-Depends: pythonX.Y-dev
	    </example>
	    where <var>X</var>.<var>Y</var> is the version used in
	    the <tt>Depends</tt>.
	  </p>
	  <p>
	    TODO: Should a <package>python-foo</package> provide
	    <package>python-foo<var>X</var>.<var>Y</var></package>,
	    provided that the Debian policy allows us to create such a
	    mass of virtual packages?
	  </p>

	</sect1>

	<sect1 id="particular_version">
	  <heading>Support a Particular Version(s)</heading>
	  <p>
	    Name your package
	    <package>python<var>X</var>.<var>Y</var>-<var>foo</var></package>
	    (a <em>versioned module package</em>). Make the dependency
	    look like
	    <example>
Depends: python<var>X</var>.<var>Y</var>
	    </example>
	    It should install modules somewhere inside
	    <file>/usr/lib/python<var>X</var>.<var>Y</var>/site-packages/</file>.
	    Any programs included should use <tt>#!/usr/bin/pythonX.Y</tt>.
	  </p>

	  <p>
	    The packaged source must declare
	    <example>
Build-Depends: pythonX.Y-dev
            </example>
	    where
	    <var>X</var>.<var>Y</var> is the version used above.
	  </p>

	  <p>
	    TODO: Describe support for multiple particular versions
	  </p>

	</sect1>

	<sect1 id="all_versions">
	  <heading>Support All/Most Versions (Including Default)</heading>
	  <p>
	    This option is only XXX available for architecture
	    dependent and independent packages. There are two
	    different cases:
	    <enumlist>
	      <item>
	        <p>Multiple versioned packages</p>
		<p>
		  You have binary extensions that must be compiled
		  against particular versions of Python.  Create
		  multiple
		  <package>python<var>X</var>.<var>Y</var>-<var>foo</var></package>
		  packages as in <ref id="particular_version">. Also
		  create an empty default package
		  <package>python-<var>foo</var></package> with
		  <example>
Depends: python (>= X.Y), python (<< X.Y+1), pythonX.Y-foo
		  </example>
		  Note that this kind of packaging means that the
		  default package will trigger a conflict when the
		  default Debian Python version in the distribution is
		  changed, and that you will have to provide a new
		  version of your package as soon as possible, since
		  the package will block the upgrade of
		  <package>python</package>.
		</p>

		<p>
		  The packaged sources <tt>Build-Depends</tt> must contain all
		  <package>python<var>X</var>.<var>Y</var>-dev</package>
		  packages that the module is built for.
		</p>
	      </item>

	      <item>A single package for all versions (NOT YET SUPPORTED!)
		<p>
		  You have a version independent Python module. Create
		  a single package
		  <package>python-<var>foo</var></package> that has a
		  dependency
		  <example>
Depends: python
		  </example>
		  It should install modules somewhere inside
		  <file>/usr/lib/python/site-packages/</file> and use
		  <tt>#!/usr/bin/python</tt> for programs. The
		  <file>postinst</file> script should create symlinks
		  in all
		  <file>/usr/lib/pythonX.Y/site-packages/</file>
		  directories that point to its
		  <file>/usr/lib/python/site-packages/</file> files
		  and compile them.
		</p>
		<p>
		  NOT YET SUPPORTED: It's errorprone if the package itself
		  supplies these scripts. And the package cannot know when a
		  new upstream Python version is installed. So the
		  <package>python<var>X</var>.<var>Y</var></package> must
		  provide these scripts, which is not yet done.
		</p>
		<p>
		  The packaged source must declare
		  <tt>Build-Depends</tt> on one
		  <package>python<var>X</var>.<var>Y</var>-dev</package>
		  package. XXX: Or build-depend on each Python
		  version, so that only checked modules are uploaded?
		</p>
		<p>
		  TODO: Should policy demand that these packages must have a
		  dependency on <package>python (<=
		  <var>X</var>.<var>Y+1</var></package>)?
		</p>
		<p>
		  DO WE WANT THIS: Some packages, which provide binary Python
		  only, package these modules together in one package (like
		  <package>python-pqueue</package>). They build-depend on all
		  used <package>python<var>X</var>.<var>Y</var>-dev</package>
		  packages, and depend on the presence of at least one of the
		  used Python versions installed, e.g.
	          <example>
Depends: python1.5 | python2.1
	          </example>
		  Also, such a package should declare
		  <tt>Provides</tt> for
		  <package>python<var>X</var>.<var>Y</var>-<var>foo</var></package>
		  for all versions provided by the package.
		</p>

	      </item>
	    </enumlist>

	  </p>
	</sect1>
	</sect>

      <sect id="package_names">
	<heading>Module Package Names</heading>
	<p>
	  Python module packages should be named for the primary module
	  provided.  The naming convention for a module <tt>foo</tt> is
	  <package>python-<var>foo</var></package> for the package for the
	  default Python version (the <em>default module package</em>).
	  (Packages which include multiple modules may additionally include
	  provides for those modules using the same convention.)
	</p>
	<p>
	  Python module packages packaged for one particular version of Python
	  (<em>versioned modules packages</em>) should be named
	  <package>python<var>X</var>.<var>Y</var>-foo</package>.
	</p>
      </sect>

      <sect id="dependencies">
	<heading>Dependencies</heading>
	<p>
	  Packaged modules available for the default Python version as
	  described in in <ref id="default_version"> must depend on
	  "<package>python (&gt;= <var>X</var>.<var>Y</var>)</package>,
	  <package>python (&lt;&lt; <var>X</var>.<var>Y+1</var>)</package>".
	</p>
	<p>
	  Packaged modules available for one particular version of Python must
	  depend on the corresponding
	  <package>python<var>X</var>.<var>Y</var></package> package instead.
	</p>
      </sect>

    <chapt id="programs">
      <heading>Python Programs</heading>

      <sect id="version_indep_progs">
	<heading>Version Independent Programs</heading>
	<p>
	  Programs that can run with any version of Python should be started
	  with <tt>#!/usr/bin/python</tt>.  They must also specify a
	  dependency on <package>python</package>.

	  You're free to use <tt>#!/usr/bin/env python</tt>, if you'd like to
	  give the user a chance to override the Debian Python package with a
	  local version.
	</p>
      </sect>

      <sect id="version_dep_progs">
	<heading>Version Dependent Programs</heading>
	<p>
	  Programs which require a specific version of Python must start with
	  <tt>#!/usr/bin/python<var>X</var>.<var>Y</var></tt>.  They must also
	  specify a dependency on
	  <package>python<var>X</var>.<var>Y</var></package>.

	  Again, if you're using <tt>#!/usr/bin/env
	  python<var>X</var>.<var>Y</var></tt>, please be aware that a user
	  might override the Debian Python package with a local version.
	</p>
      </sect>

    </chapt>


    <chapt id="embed">
      <heading>Programs Embedding Python</heading>

      <sect id="build_embedded">
	<heading>Building Embedded Programs</heading>
	<p>
	  Programs which embed a Python interpreter must declare a
	  <tt>Build-Depends</tt> on
	  <package>python<var>X</var>.<var>Y</var>-dev</package>.
	</p>
	<p>
	  TODO: Be more verbose. How about versions...
	</p>
      </sect>

      <sect id="embedded_deps">
	<heading>Embedded Python Dependencies</heading>
	<p>
	  Dependencies for programs linking against the shared Python
	  library will be automatically created by
	  <prgn>dpkg-shlibdeps</prgn>.
	</p>
      </sect>
    </chapt>

    <chapt id="other">
      <heading>Interaction with Locally Installed Python Versions</heading>

      <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 subrelease of the version of python
	you've got installed, you'll need to be careful to install all
	the modules you use for that version of python too.
      </p>

    </chapt>

    <appendix id="build_dependencies">
      <heading>Build Dependencies</heading>
      <p>
	Build dependencies for Python dependent packages must be
	declared for every Python version, that the package is built
	for. To build for a specific version, add the versioned
	dependencies, to build for the default version, add the
	unversioned dependency.

	Architecture dependent packages must depend on the
	<package>-dev</package> package; for architecture independent
	packages, it may be sufficient to depend on the
	<package>python</package> or
	<package>python<var>X</var>.<var>Y</var></package> package.
      </p>
      <p>
	Build-Depend on at least:
	<example>
Build-Depends: python1.5
Build-Depends: python2 (>= 2.0.1-1.2)
Build-Depends: python2.1
Build-Depends: python2.2 (>= 2.1.99-2)

Build-Depends: python1.5-dev (>= 1.5.2-18.6)
Build-Depends: python1.5-distutils
Build-Depends: python2-dev (>= 2.0.1-1.2)
Build-Depends: python2.1-dev (>= 2.1.1-1.4)
Build-Depends: python2.2-dev (>= 2.1.99-2)
	</example>
      </p>
    </appendix>

    <appendix id="upgrade">
      <heading>Upgrade Procedure</heading>
      <p>
	This section describes the procedure for the upgrade from the current
	<package>python-<var>XXX</var> (1.5)</package> packages to the
	<package>python1.5-<var>XXX</var></package> packages, the removal of
	the <package>python2-<var>XXX</var></package> packages and the upgrade
	to the recent <package>python2.1-<var>XXX</var></package> packages:
      </p>
      <p>
	<enumlist>
	  <item>
	    <p>
	      The Debian Python maintainer decides for the default Debian
	      Python version. In the following we assume that
	      <tt>python2.1</tt> will be the default (hint, hint ...).
	    </p>
	    <p>
	      Serious issues with the python-policy should be resolved, the
	      policy should be submitted to debian-policy.
	    </p>
	  </item>
	  <item>
	    <p>
	      Upload python core packages <package>python-<var>module</var>
	      (2.1)</package> & Co depending on
	      <package>python2.1-<var>module</var></package>.
	    </p>
	    <p>
	      The new packages will conflict with every Python dependent
	      package, that does depend on <package>python</package>,
	      <package>python-base</package>, without depending on
	      <package>python (<< 1.6)</package> or <package>python-base (<<
	      2.1)</package>.
	    </p>
	  </item>
	  <item>
	    <p>
	      At this point other python modules/packages can be made, which
	      follow the proposed policy.  Notify the maintainers of packages,
	      that the new packages conflict with.
	    </p>
	    <p>
	      We propose to make more than one source package for
	      support of more than one python version. Build 2.1 (and
	      probably 2.2) dependent packages from one source
	      packages, and 1.5 and 2.0 packages from another source
	      package (if you support these versions at all). This
	      makes it easy to remove the old packages from
	      testing/unstable.
	    </p>
	    <p>
	      XXX Do we allow NMUs which only fix the dependencies?
	    </p>
	  </item>
	  <item>
	    <p>
	      File bug report against packages and/or make NMU's for packages
	      that are not adapted by their maintainer.
	    </p>
	  </item>
	  <item>
	    <p>
	      If maintainer A (maintaining
	      <package>python-foo</package> (depending on
	      <package>python (&gt;= 2.1)</package>, <package>python
	      (&lt;&lt; 2.2))</package> decides for <ref
	      id="default_version">, then a maintainer B should be
	      allowed to repackage <package>python1.5-foo</package>,
	      if "his" package cannot be converted to use the default
	      Python version.
	    </p>
	  </item>
	  <item>
	    <p>
	      File reports that <tt>python2.0</tt> should go away,
	      file serious reports against all the
	      <package>python2-*</package> the packages and
	      <package>ftp.debian.org</package>.
	    </p>
	  </item>
	  <item>
	    <p>
	    Hopefully release woody with <tt>python2.1</tt> as the default
	    Python version.
	  </p>
	  </item>
	</enumlist>
      </p>
    </appendix>
  </book>
</debiandoc>