|Title:||Removing support for little used platforms|
|Author:||Martin von Löwis <martin at v.loewis.de>, Brett Cannon <brett at python.org>|
|Post-History:||18-Aug-2007 16-May-2014 20-Feb-2015|
This PEP documents how an operating system (platform) becomes supported in CPython and documents past support.
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.
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 . 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.
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.
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 has established a policy called product support lifecycle . 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).
- Name: MS-DOS, MS-Windows 3.xUnsupported in: Python 2.0Code removed in: Python 2.1
- Name: SunOS 4Unsupported in: Python 2.3Code removed in: Python 2.4
- Name: DYNIXUnsupported in: Python 2.3Code removed in: Python 2.4
- Name: dguxUnsupported in: Python 2.3Code removed in: Python 2.4
- Name: MinixUnsupported in: Python 2.3Code removed in: Python 2.4
- Name: Irix 4 and --with-sgi-dlUnsupported in: Python 2.3Code removed in: Python 2.4
- Name: Linux 1Unsupported in: Python 2.3Code removed in: Python 2.4
- Name: Systems defining __d6_pthread_create (configure.in)Unsupported in: Python 2.3Code removed in: Python 2.4
- Name: Systems defining PY_PTHREAD_D4, PY_PTHREAD_D6, or PY_PTHREAD_D7 in thread_pthread.hUnsupported in: Python 2.3Code removed in: Python 2.4
- Name: Systems using --with-dl-dldUnsupported in: Python 2.3Code removed in: Python 2.4
- Name: Systems using --without-universal-newlines,Unsupported in: Python 2.3Code removed in: Python 2.4
- Name: MacOS 9Unsupported in: Python 2.4Code removed in: Python 2.4
- Name: Systems using --with-wctype-functionsUnsupported in: Python 2.6Code removed in: Python 2.6
- Name: Win9x, WinME, NT4Unsupported in: Python 2.6 (warning in 2.5 installer)Code removed in: Python 2.6
- Name: AtheOSUnsupported 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
- Name: BeOSUnsupported 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 ThreadsUnsupported in: Python 3.2Code removed in: Python 3.3
- Name: SunOS lightweight processes (LWP)Unsupported in: Python 3.2Code removed in: Python 3.3
- Name: Systems using --with-pth (GNU pth threads)Unsupported in: Python 3.2Code removed in: Python 3.3
- Name: Systems using Irix threadsUnsupported in: Python 3.2Code removed in: Python 3.3
- Name: OSF* systems (issue 8606)Unsupported in: Python 3.2Code removed in: Python 3.3
- Name: OS/2 (issue 16135)Unsupported in: Python 3.3Code removed in: Python 3.4
- Name: VMS (issue 16136)Unsupported in: Python 3.3Code removed in: Python 3.4
- Name: Windows 2000Unsupported in: Python 3.3Code removed in: Python 3.4
- Name: Windows systems where COMSPEC points to command.comUnsupported in: Python 3.3Code removed in: Python 3.4
- Name: RISC OSUnsupported in: Python 3.0 (some code actually removed)Code removed in: Python 3.4
This document has been placed in the public domain.
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