PEP: 11
Title: Removing support for little used platforms
Version: $Revision$
Last-Modified: $Date$
Author: Martin von Löwis <martin@v.loewis.de>,
        Brett Cannon <brett@python.org>
Status: Active
Type: Process
Content-Type: text/x-rst
Created: 07-Jul-2002
Post-History: 18-Aug-2007
              16-May-2014
              20-Feb-2015


Abstract
--------

This PEP documents how an operating system (platform) becomes
supported in CPython and documents past support.


Rationale
---------

Over time, the CPython source code has collected various pieces of
platform-specific code, which, at some point in time, was
considered necessary to use Python on a specific platform.
Without access to this platform, it is not possible to determine
whether this code is still needed.  As a result, this code may
either break during Python's evolution, or it may become
unnecessary as the platforms evolve as well.

The growing amount of these fragments poses the risk of
unmaintainability: without having experts for a large number of
platforms, it is not possible to determine whether a certain
change to the CPython source code will work on all supported
platforms.

To reduce this risk, this PEP specifies what is required for a
platform to be considered supported by Python as well as providing a
procedure to remove code for platforms with few or no Python
users.

Supporting platforms
--------------------

Gaining official platform support requires two things. First, a core
developer needs to volunteer to maintain platform-specific code. This
core developer can either already be a member of the Python
development team or be given contributor rights on the basis of
maintaining platform support (it is at the discretion of the Python
development team to decide if a person is ready to have such rights
even if it is just for supporting a specific platform).

Second, a stable buildbot must be provided [2]_. This guarantees that
platform support will not be accidentally broken by a Python core
developer who does not have personal access to the platform. For a
buildbot to be considered stable it requires that the machine be
reliably up and functioning (but it is up to the Python core
developers to decide whether to promote a buildbot to being
considered stable).

This policy does not disqualify supporting other platforms
indirectly. Patches which are not platform-specific but still done to
add platform support will be considered for inclusion. For example,
if platform-independent changes were necessary in the configure
script which were motivated to support a specific platform that could
be accepted. Patches which add platform-specific code such as the
name of a specific platform to the configure script will generally
not be accepted without the platform having official support.

CPU architecture and compiler support are viewed in a similar manner
as platforms. For example, to consider the ARM architecture supported
a buildbot running on ARM would be required along with support from
the Python development team. In general it is not required to have
a CPU architecture run under every possible platform in order to be
considered supported.

Unsupporting platforms
----------------------

If a certain platform that currently has special code in CPython is
deemed to be without enough Python users or lacks proper support from
the Python development team and/or a buildbot, a note must be posted
in this PEP that this platform is no longer actively supported.  This
note must include:

- the name of the system
- the first release number that does not support this platform
  anymore, and
- the first release where the historical support code is actively
  removed

In some cases, it is not possible to identify the specific list of
systems for which some code is used (e.g. when autoconf tests for
absence of some feature which is considered present on all
supported systems).  In this case, the name will give the precise
condition (usually a preprocessor symbol) that will become
unsupported.

At the same time, the CPython source code must be changed to
produce a build-time error if somebody tries to install Python on
this platform.  On platforms using autoconf, configure must fail.
This gives potential users of the platform a chance to step
forward and offer maintenance.


Re-supporting platforms
-----------------------

If a user of a platform wants to see this platform supported
again, he may volunteer to maintain the platform support.  Such an
offer must be recorded in the PEP, and the user can submit patches
to remove the build-time errors, and perform any other maintenance
work for the platform.

Microsoft Windows
-----------------

Microsoft has established a policy called product support lifecycle
[1]_. Each product's lifecycle has a mainstream support phase, where
the product is generally commercially available, and an extended
support phase, where paid support is still available, and certain bug
fixes are released (in particular security fixes).

CPython's Windows support now follows this lifecycle. A new feature
release X.Y.0 will support all Windows releases whose extended support
phase is not yet expired. Subsequent bug fix releases will support
the same Windows releases as the original feature release (even if
the extended support phase has ended).

Because of this policy, no further Windows releases need to be listed
in this PEP.

Each feature release is built by a specific version of Microsoft
Visual Studio. That version should have mainstream support when the
release is made. Developers of extension modules will generally need
to use the same Visual Studio release; they are concerned both with
the availability of the versions they need to use, and with keeping
the zoo of versions small. The CPython source tree will keep
unmaintained build files for older Visual Studio releases, for which
patches will be accepted. Such build files will be removed from the
source tree 3 years after the extended support for the compiler has
ended (but continue to remain available in revision control).

Legacy C Locale
---------------

Starting with CPython 3.7.0, \*nix platforms are expected to provide
at least one of ``C.UTF-8`` (full locale), ``C.utf8`` (full locale) or
``UTF-8`` (``LC_CTYPE``-only locale) as an alternative to the legacy ``C``
locale.

Any Unicode-related integration problems that occur only in the legacy ``C``
locale and cannot be reproduced in an appropriately configured non-ASCII
locale will be closed as "won't fix".

No-longer-supported platforms
-----------------------------

* | Name:             MS-DOS, MS-Windows 3.x
  | Unsupported in:   Python 2.0
  | Code removed in:  Python 2.1

* | Name:             SunOS 4
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             DYNIX
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             dgux
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             Minix
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             Irix 4 and --with-sgi-dl
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             Linux 1
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             Systems defining __d6_pthread_create (configure.in)
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             Systems defining PY_PTHREAD_D4, PY_PTHREAD_D6,
                      or PY_PTHREAD_D7 in thread_pthread.h
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             Systems using --with-dl-dld
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             Systems using --without-universal-newlines,
  | Unsupported in:   Python 2.3
  | Code removed in:  Python 2.4

* | Name:             MacOS 9
  | Unsupported in:   Python 2.4
  | Code removed in:  Python 2.4

* | Name:             Systems using --with-wctype-functions
  | Unsupported in:   Python 2.6
  | Code removed in:  Python 2.6

* | Name:             Win9x, WinME, NT4
  | Unsupported in:   Python 2.6 (warning in 2.5 installer)
  | Code removed in:  Python 2.6

* | Name:             AtheOS
  | Unsupported in:   Python 2.6 (with "AtheOS" changed to "Syllable")
  | Build broken in:  Python 2.7 (edit configure to reenable)
  | Code removed in:  Python 3.0
  | Details:          http://www.syllable.org/discussion.php?id=2320

* | Name:             BeOS
  | Unsupported in:   Python 2.6 (warning in configure)
  | Build broken in:  Python 2.7 (edit configure to reenable)
  | Code removed in:  Python 3.0

* | Name:             Systems using Mach C Threads
  | Unsupported in:   Python 3.2
  | Code removed in:  Python 3.3

* | Name:             SunOS lightweight processes (LWP)
  | Unsupported in:   Python 3.2
  | Code removed in:  Python 3.3

* | Name:             Systems using --with-pth (GNU pth threads)
  | Unsupported in:   Python 3.2
  | Code removed in:  Python 3.3

* | Name:             Systems using Irix threads
  | Unsupported in:   Python 3.2
  | Code removed in:  Python 3.3

* | Name:             OSF* systems (issue 8606)
  | Unsupported in:   Python 3.2
  | Code removed in:  Python 3.3

* | Name:             OS/2 (issue 16135)
  | Unsupported in:   Python 3.3
  | Code removed in:  Python 3.4

* | Name:             VMS (issue 16136)
  | Unsupported in:   Python 3.3
  | Code removed in:  Python 3.4

* | Name:             Windows 2000
  | Unsupported in:   Python 3.3
  | Code removed in:  Python 3.4

* | Name:             Windows systems where COMSPEC points to command.com
  | Unsupported in:   Python 3.3
  | Code removed in:  Python 3.4

* | Name:             RISC OS
  | Unsupported in:   Python 3.0 (some code actually removed)
  | Code removed in:  Python 3.4

* | Name:             IRIX
  | Unsupported in:   Python 3.7
  | Code removed in:  Python 3.7

* | Name:             Systems without multithreading support
  | Unsupported in:   Python 3.7
  | Code removed in:  Python 3.7

References
----------

.. [1] http://support.microsoft.com/lifecycle/
.. [2] http://buildbot.python.org/3.x.stable/

Copyright
---------

This document has been placed in the public domain.


..
   Local Variables:
   mode: indented-text
   indent-tabs-mode: nil
   sentence-end-double-space: t
   fill-column: 70
   coding: utf-8
   End:
