Resent: I've sent the message below to debian-python@, but it hits the
100 kB size limit; instead, please consult the git branch at:
http://git.debian.org/?p=users/lool/python-defaults.git;a=shortlog;h=refs/tags/current-practices-v2
Hi
This a revised patchset with updates to address various comments
received via email or IRC. Original announcement:
http://lists.debian.org/debian-python/2009/12/msg00009.html
I'm attaching the latest version of all patches and the updated
generated text.
Thanks,
--
Loïc Minier
Debian Python Policy
--------------------
Neil Schemenauer <nas@debian.org>
Matthias Klose <doko@debian.org>
Gregor Hoffleit <flight@debian.org>
Josselin Mouette <joss@debian.org>
Joe Wreschnig <piman@debian.org>
Loi"c Minier <lool@debian.org>
Scott Kitterman <scott@kitterman.com>
version 0.9.0.0
-------------------------------------------------------------------------------
Abstract
--------
This document describes the packaging of Python within the Debian
GNU/Linux distribution and the policy requirements for packaged Python
programs and modules.
Copyright Notice
----------------
Copyright (C) 1999, 2001, 2003, 2006, 2009 Software in the Public
Interest
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.
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.
A copy of the GNU General Public License is available as
`/usr/share/common-licences/GPL' in the Debian GNU/Linux distribution
or on the World Wide Web at The GNU General Public License
(http://www.gnu.org/copyleft/gpl.html).
You can also obtain it by writing to the Free Software Foundation,
Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
-------------------------------------------------------------------------------
Contents
--------
1. Python Packaging
1.1. Versions
1.2. Main packages
1.3. Minimal packages
1.4. Python Interpreter
1.4.1. Interpreter Name
1.4.2. Interpreter Location
1.5. Module Path
1.6. Hooks for updates to installed runtimes
1.7. Documentation
2. Packaged Modules
2.1. Types of Python Modules
2.2. Module Package Names
2.3. Specifying Supported Versions
2.4. Dependencies
2.5. Provides
2.6. Modules Byte-Compilation
3. Python Programs
3.1. Programs using the default python
3.1.1. Programs Shipping Private Modules
3.2. Programs Using a Particular Python Version
4. Programs Embedding Python
4.1. Building Embedded Programs
4.2. Embedded Python Dependencies
5. Interaction with Locally Installed Python Versions
A. Build Dependencies
B. Packaging Tools
B.1. distutils
B.2. python-support
B.3. python-central
B.4. CDBS
C. Upgrade Procedure
-------------------------------------------------------------------------------
1. Python Packaging
-------------------
1.1. Versions
-------------
At any given time, the binary package `python' will represent the
current default Debian Python version.
The default Debian Python version should always be the latest stable
upstream release that can be fully integrated in the distribution.
There may be newer supported or unsupported versions included in the
distribution if they are not fully integrated for a particular
release.
Apart from the default version, legacy versions of Python or beta
versions of future releases 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 2.5 and 2.5.1 are sub-minor versions of the same Python version
2.5, but Python 2.4 and 2.5 are indeed different versions.)
For any version, the main binary package must be called
`python<X>.<Y>'.
The set of currently supported python versions can be found in
`/usr/share/python/debian_defaults'. This file is in Python
ConfigParser format and defines four variables in its DEFAULT section:
default-version which is the current default Python runtime,
supported-versions which is the set of runtimes currently supported
and for which modules should be built and byte-compiled, old-versions
which is the list of runtimes which might still be on the system but
for which should not be built anymore, and unsupported-versions which
is the list of runtimes which should not be supported at all, that is
modules should not be built or byte-compiled for these.
unsupported-versions is a superset of (includes) old-versions and the
default-version is always in supported-versions.
Newer versions might also appear in unsupported-versions before being
moved to supported-versions.
1.2. Main packages
------------------
For every Python version provided in the distribution, the binary
package `python<X>.<Y>' shall provide a complete distribution for
_deployment_ of Python scripts and applications. The package must
ensure that the `/usr/bin/python<X>.<Y>' interpreter executable is
provided.
Installation of `python<X>.<Y>' shall provide the modules of the
upstream Python distribution with some exceptions.
Excluded are modules that cannot be included for licensing reasons
(for example the profile module), for dependency tracking purposes
(for example the GPL-licensed gdbm module) or that should not be
included for packaging reasons (for example the tk module which
depends on Xorg). Some tools and files for the _development_ of
Python modules are split off in a separate binary package
`python<X>.<Y>-dev'. Documentation will be provided separately as
well.
At any time, the `python' binary package must ensure that
`/usr/bin/python' is provided as a symlink to the current
`python<X>.<Y>' executable. The `python' binary package must also
depend on the appropriate `python<X>.<Y>' to ensure this runtime is
installed.
The version of the `python' binary package must be greater than or
equal to <X>.<Y> and smaller than <X>.<Y+1>.
1.3. Minimal packages
---------------------
For every Python version provided in the distribution, the binary
package `python<X>.<Y>'-minimal might exist and should not be depended
upon by other packages except the Python runtime packages themselves.
1.4. Python Interpreter
-----------------------
1.4.1. Interpreter Name
-----------------------
Python scripts depending on the default Python version (see Section
1.2, `Main packages') or not depending on a specific Python version
should use `python' (without a version) as the interpreter name.
Python scripts that only work with a specific Python version must
explicitly use the versioned interpreter name (`python<X>.<Y>').
1.4.2. Interpreter Location
---------------------------
The preferred specification for the Python interpreter is
`/usr/bin/python' or `/usr/bin/python<X>.<Y>'. This ensures that a
Debian installation of python is used and all dependencies on
additional python modules are met.
If a maintainer would like to provide the user with the possibility to
override the Debian Python interpreter, he may want to use
`/usr/bin/env python' or `/usr/bin/env python<X>.<Y>'. However this
is not advisable as it bypasses Debian's dependency checking and makes
the package vulnerable to incomplete local installations of python.
1.5. Module Path
----------------
By default, Python modules are searched in the directories listed in
the PYTHONPATH environment variable and in the sys.path Python
variable. Since python2.4 version 2.4.5-3, python2.5 version 2.5.2-7,
and python2.6 version 2.6.2-1 sys.path does not include a
/usr/lib/python<X><Y>.zip entry anymore. Directories with private
Python modules must be absent from the sys.path. Public Python
modules not handled by python-central or python-support must be
installed in the system Python modules directory,
/usr/lib/python<X>.<Y>/dist-packages for python2.6 and later, and
/usr/lib/python<X>.<Y>/site-packages for python2.5 and earlier. As an
exception to the above, modules managed by python-support are
installed in another directory which is added to the sys.path using
the .pth mechanism. The .pth mechanism is documented in the Python
documentation of the `site' module. A special directory is dedicated
to public Python modules installed by the local administrator,
/usr/local/lib/python<X>.<Y>/dist-packages for python2.6 and later,
and /usr/local/lib/python<X>.<Y>/site-packages for python2.5 and
earlier. For a local installation by the administrator of python2.6
and later, a special directory is reserved to Python modules which
should only be available to this Python,
/usr/local/lib/python<X>.<Y>/site-packages. Unfortunately, for
python2.5 and earlier this directory is also visible to the system
Python. Additional information on appending site-specific paths to
the module search path is available in the official documentation of
the site module.
When binary packages ship identical source code for multiple Python
versions, for instance /usr/lib/python2.6/dist-packages/foo.py and
/usr/lib/python2.5/site-packages/foo.py, these should point to a
common file. A common location to share, across Python versions,
arch-independent files which would otherwise go to the directory of
system public modules is /usr/share/pyshared.
1.6. Hooks for updates to installed runtimes
--------------------------------------------
The `python' binary package has special hooks to allow other packages
to act upon updates to the installed runtimes. This mechanism is
required to handle changes of the default Python runtime in some
packages and to enable the Python packaging helpers. 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.
1. /usr/share/python/runtime.d/*.rtinstall: these are called when a
runtime is installed or becomes supported. The first argument is
"rtinstall", the second argument is the affected runtime (for
example python<X>.<Y>) and the third and fourth argument are the
old and new version of this packaged runtime if this runtime was
already installed but unsupported.
2. /usr/share/python/runtime.d/*.rtremove: these are called when a
runtime is installed or stops being supported. The first
argument is "rtremove", and the second argument is the affected
runtime (for example python<X>.<Y>).
3. /usr/share/python/runtime.d/*.rtupate: these are called when the
default runtime changes. The first argument is either
"pre-rtupdate", called before changing the default runtime, or
"rtupdate", called when changing the default runtime, or
"post-rtupdate", called immediately afterwards. The second
argument is the old default runtime (for example python<X>.<Y>),
and the third argument is the new default runtime (for example
python<X>.<Z>).
1.7. Documentation
------------------
Python documentation is split out in separate binary packages
`python<X>.<Y>-doc'. The binary package `python-doc' will always
provide the documentation for the default Debian Python version.
TODO: Policy for documentation of third party packages.
-------------------------------------------------------------------------------
2. Packaged Modules
-------------------
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-byte-compiling pyc and pyo files) or shortly thereafter with
automated rebuilds (to handle C extensions). These policies encourage
automated dependency generation and loose version bounds whenever
possible.
2.1. Types of Python Modules
----------------------------
There are two kinds of Python modules, "pure" Python modules, and
extension modules. Pure Python modules are Python source code that
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. Some distributions link
extensions to libpython, but this is not the case in Debian as symbols
might as well be resolved by `/usr/bin/python<X>.<Y>' which is not
linked to libpython.
Python packages are directories containing at least a `__init__.py',
other modules, extensions and packages (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.
There are two ways to distribute Python modules. Public modules are
installed in a public directory as listed in Section 1.5, `Module
Path'. They are accessible to any program. Private modules are
installed in a private directory such as `/usr/share/<package-name>'
or `/usr/lib/<package-name>'. They are generally only accessible to a
specific program or suite of programs included in the same package.
2.2. Module Package Names
-------------------------
Public modules used by other packages must have their binary package
name prefixed with <python->. It is recommended to use this prefix
for all packages with public modules as they be used by other packages
in the future. The binary package for module foo should preferably be
named `python-<foo>', if the module name allows, but this is not
required if the binary package ships multiple modules. In the latter
case the maintainer choses the name of the module which represents the
package the most. Such a package should support the current Debian
Python version, and more if possible (there are several tools to help
implement this, see Appendix B, `Packaging Tools'). For example, if
Python 2.3, 2.4, and 2.5 are supported, the Python command
import foo
should import the module when the user is running any of
`/usr/bin/python2.3', `/usr/bin/python2.4', and `/usr/bin/python2.5'.
This requirement also applies to extension modules; binaries for all
the supported Python versions should be included in a single package.
2.3. Specifying Supported Versions
----------------------------------
The optional `XS-Python-Version' field in `debian/control' specifies
the versions of Python supported by the source package. When not
specified, it defaults to all currently supported Python versions. It
is notably used to track packages during Python transitions, and is
also used by some packaging scripts to automatically generate
appropriate Depends and Provides lines. The format of the field may
be one of the following:
XS-Python-Version: >= X.Y
XS-Python-Version: >= A.B, << X.Y
XS-Python-Version: A.B, X.Y
XS-Python-Version: all
The keyword "all" means that the package supports any Python version
available but might be deprecated in the future since using version
numbers is clearer than "all" and encodes more information. The
keyword "current" has been deprecated and used to mean that the
package would only have to support a single version (even across
default version changes).
Your control file should also have a line:
XB-Python-Version: ${python:Versions}
The python:Versions is substituted by the supported Python versions of
the binary package, based on `XS-Python-Version'. (If you are not
using python-central or python-support, you will need to handle this
substitution yourself.) The format of the field `XB-Python-Version' is
the same as the `XS-Python-Version' field for packages not containing
extensions. Packages with extensions must list the versions
explicitly.
If your package is used by another module or application that requires
a specific Python version, it should also `Provide: python<X>.<Y>-foo'
for each version it supports.
2.4. Dependencies
-----------------
Packaged modules available for the default Python version (or many
versions including the default) as described in Section 2.2, `Module
Package Names' must depend on "`python (>= <X>.<Y>')". If they
require other modules to work, they must depend on the corresponding
`python-foo'. They must not depend on any `python<X>.<Y>-foo'.
Packaged modules available for one particular version of Python must
depend on the corresponding `python<X>.<Y>' package instead. If they
need other modules, they must depend on the corresponding
`python<X>.<Y>-foo' packages, and must not depend on any `python-foo'.
2.5. Provides
-------------
Provides in binary packages of the form `python-<foo>' must be
specified, if the package contains an extension for more than one
python version. Provides should also be added on request of
maintainers who depend on a non-default python version.
2.6. Modules Byte-Compilation
-----------------------------
If a binary package provides any binary-independent modules (`foo.py'
files), the corresponding byte-compiled modules (`foo.pyc' files) and
optimized modules (`foo.pyo' files) must not ship in the package.
Instead, they should be generated in the package's postinst, and
removed in the package's prerm. The package's prerm has to make sure
that both `foo.pyc' and `foo.pyo' are removed.
A binary package should only byte-compile the files which belong to
the package.
The file `/etc/python/debian_config' allows configuration how modules
should be byte-compiled. The postinst scripts should respect these
settings.
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. Public
Python extensions should be bin-NMUed. Private Python extensions
should be subject to binary NMUs every time the default interpreter
changes, unless the extension is updated through a .rtupdate script.
-------------------------------------------------------------------------------
3. Python Programs
------------------
3.1. Programs using the default python
--------------------------------------
Programs that can run with any version of Python must begin with
`#!/usr/bin/python' or `#!/usr/bin/env python' (the former is
preferred). They must also specify a dependency on `python', with a
versioned dependency if necessary.
If the program needs the python module `foo', it must depend on the
real package providing this module, usually `python-foo' but this name
might vary when the package ships multiple modules.
3.1.1. Programs Shipping Private Modules
----------------------------------------
A program using `/usr/bin/python' as interpreter can come up with
private Python modules. These modules should be installed in
`/usr/share/<module>', or `/usr/lib/<module>' if the modules are
architecture-dependent (e.g. extensions).
The rules explained in Section 2.6, `Modules Byte-Compilation' 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 postinst, using the current default Python version, and
removed in the prerm. Modules should be byte-compiled using the
current default Python version.
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. `Depends: python (>= 2.4), python
(<= 2.5)'. No tools currently exist to alleviate this situation.
3.2. Programs Using a Particular Python Version
-----------------------------------------------
A program which requires a specific version of Python must begin with
`#!/usr/bin/python<X>.<Y>' (or `#!/usr/bin/env python<X>.<Y>'). It
must also specify a dependency on `python<X>.<Y>' and on any
`python<X>.<Y>-foo' package providing necessary modules. It should
not depend on any `python-foo' package, unless it requires a specific
version of the package (since virtual packages cannot be versioned).
If this is the case, it should depend on both the virtual package and
the main package (e.g. `Depends: python2.4-foo, python-foo (>=
1.0)').
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.
-------------------------------------------------------------------------------
4. Programs Embedding Python
----------------------------
4.1. Building Embedded Programs
-------------------------------
Programs which embed a Python interpreter must declare a
`Build-Depends' on `python<X>.<Y>-dev', where python<X>.<Y> 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.
4.2. Embedded Python Dependencies
---------------------------------
Dependencies for programs linking against the shared Python library
will be automatically created by `dpkg-shlibdeps'. The
`libpython<X>.<Y>.so.<Z>' library the program is built against is
provided by the `python<X>.<Y>' package.
-------------------------------------------------------------------------------
5. Interaction with Locally Installed Python Versions
-----------------------------------------------------
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.
If you install a different sub-release 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.
-------------------------------------------------------------------------------
A. Build Dependencies
---------------------
Build dependencies for Python dependent packages must be declared for
every Python version that the package is built for. The
`python-all-dev' should be used when building modules for any or all
Python versions. To build for a specific version or versions,
Build-Depend on `python<X>.<Y>-dev'.
Some applications and pure Python modules may be able to build-depend
only on `python' or `python-all' and not require the -dev packages.
Build-Depend on at least:
Build-Depends: python2.3 (>= 2.3-1)
Build-Depends: python2.4 (>= 2.4-1)
Build-Depends: python (>= 2.3.5-7)
Build-Depends: python-all
Build-Depends: python2.3-dev (>= 2.3-1)
Build-Depends: python2.4-dev (>= 2.4-1)
Build-Depends: python-dev (>= 2.3.5-7)
Build-Depends: python-all-dev
If you use either `python-support' or `python-central' you must
additionally Build-Depend on those.
-------------------------------------------------------------------------------
B. Packaging Tools
------------------
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.
B.1. distutils
--------------
The standard Python distutils module has been modified in Debian to
change the default installation directory of public Python modules and
to add a new flag to the "install" command to override the default,
`--install-layout='. To allow the use this flag, maintainers should
ensure that at least version 2.6.2-1 will be used for python2.6,
version 2.5.4-1 for python2.5, and version 2.4.6-2 for python2.4.
This flag is parsed but ignored in python2.4 and python2.5. Public
Python modules installed with a modified distutils default to
/usr/local/lib/python<X>.<Y>/dist-packages for python2.6 and later.
This directory is seen by the system-provided python2.6. When using a
system-provided python2.4 or python2.5, the default is
/usr/lib/python<X>.<Y>/site-packages which is seen by the
system-provided python2.4 and python2.5 versions, but not by a
system-provided python2.6 and later versions. When using a local
Python installation, the default is
/usr/local/lib/python<X>.<Y>/site-packages which is only seen by the
local Python installation. Using the `--install-layout=deb' flag to
the "install" command of `setup.py' with a system-provided python2.6
or later versions, Python modules will be installed to
/usr/lib/python<X>.<Y>/dist-packages which is only seen by the
system-provided python, not by a local installation. Using the
`--install-layout=deb' flag to `setup.py' with a system-provided
python2.4 or python2.5 does not affect the default installation
directory.
B.2. python-support
-------------------
The python-support system provides a simple way to byte-compile pure
Python modules and manage dependencies. It integrates with
`debhelper', manages byte-compilation, private modules, will properly
use the /usr/share/pyshared directory, integrates with runtime update
hooks, and will fill-in the `${python:Depends}', `${python:Versions}',
and `${python:Provides}' substvars. See the python-support
documentation in /usr/share/doc/python-support for details.
B.3. python-central
-------------------
python-central provides another way to manage Python modules. It
integrates with `debhelper', manages byte-compilation, private
modules, will properly use the /usr/share/pyshared directory,
integrates with runtime update hooks, and will fill-in the
`${python:Depends}', `${python:Versions}', and `${python:Provides}'
substvars. See the python-central documentation in the pycentral(1)
and dh_pycentral(1) man pages.
B.4. CDBS
---------
The CDBS python-distutils.mk class helps packaging of setup.py based
Python packages.
-------------------------------------------------------------------------------
C. Upgrade Procedure
--------------------
This section describes the procedure for the upgrade when the default
python version is changed in the `unstable' distribution, requiring
recompilation of many python-related packages.
1. Selected pre-releases and release candidates of new Python
versions are uploaded to Experimental to support pre-transition
work and testing.
2. Application and module maintainers make sourceful changes where
needed to prepare for the new Python version when needed.
3. Have a long and heated discussion.
4. 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 Unstable.
5. Upload of the python core meta-packages `python', `python-dev',
`python-doc' and several `python-<module>', depending on the new
`python<X>.<Y>', `python<X>.<Y>-dev' and so on.
6. The release team schedules rebuilds for packages that may need
it. Packages that require additional manual work get updated and
uploaded.
-------------------------------------------------------------------------------
Debian Python Policy
Neil Schemenauer <nas@debian.org>
Matthias Klose <doko@debian.org>
Gregor Hoffleit <flight@debian.org>
Josselin Mouette <joss@debian.org>
Joe Wreschnig <piman@debian.org>
Loi"c Minier <lool@debian.org>
Scott Kitterman <scott@kitterman.com>
version 0.9.0.0
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