Table of Contents
	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 *.pyc
	and *.pyo) or shortly thereafter with automated
	rebuilds (to handle C extensions). These policies encourage
	automated dependency generation and loose version bounds whenever
	possible.
	
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.
	  Debian Python does not link extensions to libpython
	  (as is done in some operating systems). Symbols are resolved by
	  /usr/bin/python which is not
	  linked to X.Ylibpython.
	
Python packages are a way of structuring Python’s module namespace by using “dotted module names”. See Python's glossary 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.
	  There are two ways to distribute Python modules. Public modules
	  are installed in a public directory as listed in Section 2.5, “Module Path”.
	  They are accessible to any program. Private modules are installed
	  in a private directory such
	  as /usr/share/
	  or package-name/usr/lib/. They are
	  generally only accessible to a specific program or suite of
	  programs included in the same package.
	package-name
	  PEP 427
	  defines a built-package format called "wheels", which is a Zip
	  format archive containing Python code and
	  a *.dist-info metadata directory, in a single file
	  named with the .whl suffix. As Zip files, wheels
	  containing pure Python can be put on sys.path and modules in the
	  wheel can be imported directly by Python's import
	  statement. (Importing extension modules from wheels is not yet
	  supported as of Python 3.4.)
	
	  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 sys.path, cannot be easily
	  grepped, and stack traces through Zip files are more difficult to
	  debug.
	
	  A very limited set of wheel packages are available in the archive,
	  but these support the narrow purpose of enabling
	  the pip, virtualenv,
	  and pyvenv tools in a Debian policy compliant way.
	  These packages build their own dependent wheels through the use of
	  the dirtbike "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.  Since only the programs that require wheels need build
	  them, only they may provide -whl packages,
	  e.g. python3-pip-whl.
	
	  When these binary packages are installed, *.whl files
	  must be placed in the /usr/share/python-wheels
	  directory. The location inside a virtual environment will be
	  rooted in the virtual environment, instead of /usr.
	
Public Python modules must be packages separately by major Python version, to preserve run time separation between Python 2 and Python 3.
	  Public Python 3 modules used by other packages must have their
	  binary package name prefixed with python3-.
	  Public Python 2 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 may be used by other packages in the future.
	
	  The binary package for module foo should preferably be
	  named python3- (for Python 3)
	  or foopython- (for Python 2), 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.
	foo
	  For subpackages such as foo.bar, the recommendation is
	  to name the binary
	  package python3- (for Python
	  3) or foo.barpython- (for Python 2).
	foo.bar
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 3.3, 3.4, and 3.5 are supported, the Python statement
import foo
	  should import the module when the program interpreter is any
	  of /usr/bin/python3.3, /usr/bin/python3.4,
	  and /usr/bin/python3.5. This requirement also applies
	  to extension modules; binaries for all the supported Python
	  versions should be included in a single package.
	
          Packages intended for use with Django (python3-django/
          python-django) are installed in the same namespace as
          other python packages for a variety of reasons.  Many such packages are
          named django_$name upstream.  These are then packaged as
          python3-django-$name and
          python-django-$name.
          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.
	
	  The debian/control source paragraph may contain
	  optional fields to specify the versions of Python the package
	  supports.
	
	  The optional X-Python3-Version field specifies the
	  versions of Python 3 supported. When not specified, it defaults to
	  all currently supported Python 3 versions.
	
	  Similarly, the optional fields X-Python-Version
	  or XS-Python-Version were used to specify the versions of
	  Python 2 supported by the source package. They are obsolete and
	  can be removed now that only Python 2.7 is supported.
	
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:
X-Python3-Version: >= X.Y X-Python3-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 2 version available but might be deprecated in the future
	  since using version numbers is clearer than all and
	  encodes more information. The keyword all is limited to
	  Python 2 versions and must be ignored for Python 3 versions.
	
	  A comma-separated list of multiple individual versions
	  (e.g. 3.3, 3.4, 3.5) in XS-Python-Version will
	  continue to be supported, but is not recommended. The use of
	  multiple individual versions in X-Python-Version
	  or X-Python3-Version is not supported for Wheezy and
	  later releases.
	
	  The keyword current has been deprecated and used to mean
	  that the package would only have to support a single Python 2
	  version (even across default version changes). It must be ignored
	  for Python 3 versions.
	
	  The use of XB-Python-Version in the binary package
	  paragraphs of debian/control 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.
	
Any package that installs modules for the default Python version (or many versions including the default) as described in Section 3.3, “Module Package Names”, 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.
	  For Python 3, the correct dependencies are Depends:
	  python3 (>= 3. and any
	  corresponding Y)python3- packages.
	foo
	  For Python 2, the correct dependencies are Depends:
	  python (>= 2. and any
	  corresponding Y)python- packages.
	foo
	  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. Depends:
	  python3 (<< .
	X.Y)
	  Binary packages that declare Provides dependencies of the form
	  python
	  were never supported for Python 3 and are no longer useful for
	  Python 2. They should be removed in the normal course of package
	  updates. Future provision of values for the substituation variable
	  X.Y-foopython:Provides is not guaranteed.
	
	  If a binary package provides any binary-independent modules
	  (foo.pyfoo.pycfoo.pyofoo.pycfoo.pyo
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
	  post-install 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.