[Python-Dev] PEP 514: Python registration in the Windows registry
Guido van Rossum
guido at python.org
Fri Jul 15 18:26:08 EDT 2016
I was going to delegate to our resident Windows expert, but that's you. :-(
Can you suggest someone else? I really don't want to swap in what I
once knew about the Windows registry...
On Fri, Jul 15, 2016 at 3:20 PM, Steve Dower <steve.dower at python.org> wrote:
> Hi all
>
> I'd like to get this PEP approved (status changed to Active, IIUC).
>
> So far (to my knowledge), Anaconda is writing out the new metadata and
> Visual Studio is reading it. Any changes to the schema now will require
> somewhat public review anyway, so I don't see any harm in approving the PEP
> right now.
>
> To reiterate, this doesn't require changing anything about CPython at all
> and has no backwards compatibility impact on official releases (but
> hopefully it will stop alternative distros from overwriting our essential
> metadata and causing problems).
>
> I suppose I look to Guido first, unless he wants to delegate to one of the
> other Windows contributors?
>
> Cheers,
> Steve
>
> URL: https://www.python.org/dev/peps/pep-0514/
>
> Full text
> -------
>
> PEP: 514
> Title: Python registration in the Windows registry
> Version: $Revision$
> Last-Modified: $Date$
> Author: Steve Dower <steve.dower at python.org>
> Status: Draft
> Type: Informational
> Content-Type: text/x-rst
> Created: 02-Feb-2016
> Post-History: 02-Feb-2016, 01-Mar-2016
>
> Abstract
> ========
>
> This PEP defines a schema for the Python registry key to allow third-party
> installers to register their installation, and to allow applications to
> detect
> and correctly display all Python environments on a user's machine. No
> implementation changes to Python are proposed with this PEP.
>
> Python environments are not required to be registered unless they want to be
> automatically discoverable by external tools.
>
> The schema matches the registry values that have been used by the official
> installer since at least Python 2.5, and the resolution behaviour matches
> the
> behaviour of the official Python releases.
>
> Motivation
> ==========
>
> When installed on Windows, the official Python installer creates a registry
> key
> for discovery and detection by other applications. This allows tools such as
> installers or IDEs to automatically detect and display a user's Python
> installations.
>
> Third-party installers, such as those used by distributions, typically
> create
> identical keys for the same purpose. Most tools that use the registry to
> detect
> Python installations only inspect the keys used by the official installer.
> As a
> result, third-party installations that wish to be discoverable will
> overwrite
> these values, resulting in users "losing" their Python installation.
>
> By describing a layout for registry keys that allows third-party
> installations
> to register themselves uniquely, as well as providing tool developers
> guidance
> for discovering all available Python installations, these collisions should
> be
> prevented.
>
> Definitions
> ===========
>
> A "registry key" is the equivalent of a file-system path into the registry.
> Each
> key may contain "subkeys" (keys nested within keys) and "values" (named and
> typed attributes attached to a key).
>
> ``HKEY_CURRENT_USER`` is the root of settings for the currently logged-in
> user,
> and this user can generally read and write all settings under this root.
>
> ``HKEY_LOCAL_MACHINE`` is the root of settings for all users. Generally, any
> user can read these settings but only administrators can modify them. It is
> typical for values under ``HKEY_CURRENT_USER`` to take precedence over those
> in
> ``HKEY_LOCAL_MACHINE``.
>
> On 64-bit Windows, ``HKEY_LOCAL_MACHINE\Software\Wow6432Node`` is a special
> key
> that 32-bit processes transparently read and write to rather than accessing
> the
> ``Software`` key directly.
>
> Structure
> =========
>
> We consider there to be a single collection of Python environments on a
> machine,
> where the collection may be different for each user of the machine. There
> are
> three potential registry locations where the collection may be stored based
> on
> the installation options of each environment::
>
> HKEY_CURRENT_USER\Software\Python\<Company>\<Tag>
> HKEY_LOCAL_MACHINE\Software\Python\<Company>\<Tag>
> HKEY_LOCAL_MACHINE\Software\Wow6432Node\Python\<Company>\<Tag>
>
> Environments are uniquely identified by their Company-Tag pair, with two
> options
> for conflict resolution: include everything, or give priority to user
> preferences.
>
> Tools that include every installed environment, even where the Company-Tag
> pairs
> match, should ensure users can easily identify whether the registration was
> per-user or per-machine.
>
> When tools are selecting a single installed environment from all registered
> environments, the intent is that user preferences from ``HKEY_CURRENT_USER``
> will override matching Company-Tag pairs in ``HKEY_LOCAL_MACHINE``.
>
> Official Python releases use ``PythonCore`` for Company, and the value of
> ``sys.winver`` for Tag. Other registered environments may use any values for
> Company and Tag. Recommendations are made in the following sections.
>
> Python environments are not required to register themselves unless they want
> to
> be automatically discoverable by external tools.
>
> Backwards Compatibility
> -----------------------
>
> Python 3.4 and earlier did not distinguish between 32-bit and 64-bit builds
> in
> ``sys.winver``. As a result, it is possible to have valid side-by-side
> installations of both 32-bit and 64-bit interpreters.
>
> To ensure backwards compatibility, applications should treat environments
> listed
> under the following two registry keys as distinct, even when the Tag
> matches::
>
> HKEY_LOCAL_MACHINE\Software\Python\PythonCore\<Tag>
> HKEY_LOCAL_MACHINE\Software\Wow6432Node\Python\PythonCore\<Tag>
>
> Environments listed under ``HKEY_CURRENT_USER`` may be treated as distinct
> from
> both of the above keys, potentially resulting in three environments
> discovered
> using the same Tag. Alternatively, a tool may determine whether the per-user
> environment is 64-bit or 32-bit and give it priority over the per-machine
> environment, resulting in a maximum of two discovered environments.
>
> It is not possible to detect side-by-side installations of both 64-bit and
> 32-bit versions of Python prior to 3.5 when they have been installed for the
> current user. Python 3.5 and later always uses different Tags for 64-bit and
> 32-bit versions.
>
> Environments registered under other Company names must use distinct Tags to
> support side-by-side installations. Tools consuming these registrations are
> not required to disambiguate tags other than by preferring the user's
> setting.
>
> Company
> -------
>
> The Company part of the key is intended to group related environments and to
> ensure that Tags are namespaced appropriately. The key name should be
> alphanumeric without spaces and likely to be unique. For example, a
> trademarked
> name, a UUID, or a hostname would be appropriate::
>
> HKEY_CURRENT_USER\Software\Python\ExampleCorp
> HKEY_CURRENT_USER\Software\Python\6C465E66-5A8C-4942-9E6A-D29159480C60
> HKEY_CURRENT_USER\Software\Python\www.example.com
>
> The company name ``PyLauncher`` is reserved for the PEP 397 launcher
> (``py.exe``). It does not follow this convention and should be ignored by
> tools.
>
> If a string value named ``DisplayName`` exists, it should be used to
> identify
> the environment category to users. Otherwise, the name of the key should be
> used.
>
> If a string value named ``SupportUrl`` exists, it may be displayed or
> otherwise
> used to direct users to a web site related to the environment.
>
> A complete example may look like::
>
> HKEY_CURRENT_USER\Software\Python\ExampleCorp
> (Default) = (value not set)
> DisplayName = "Example Corp"
> SupportUrl = "http://www.example.com"
>
> Tag
> ---
>
> The Tag part of the key is intended to uniquely identify an environment
> within
> those provided by a single company. The key name should be alphanumeric
> without
> spaces and stable across installations. For example, the Python language
> version, a UUID or a partial/complete hash would be appropriate; an integer
> counter that increases for each new environment may not::
>
> HKEY_CURRENT_USER\Software\Python\ExampleCorp\3.6
> HKEY_CURRENT_USER\Software\Python\ExampleCorp\6C465E66
>
> If a string value named ``DisplayName`` exists, it should be used to
> identify
> the environment to users. Otherwise, the name of the key should be used.
>
> If a string value named ``SupportUrl`` exists, it may be displayed or
> otherwise
> used to direct users to a web site related to the environment.
>
> If a string value named ``Version`` exists, it should be used to identify
> the
> version of the environment. This is independent from the version of Python
> implemented by the environment.
>
> If a string value named ``SysVersion`` exists, it must be in ``x.y`` or
> ``x.y.z`` format matching the version returned by ``sys.version_info`` in
> the
> interpreter. Otherwise, if the Tag matches this format it is used. If not,
> the
> Python version is unknown.
>
> Note that each of these values is recommended, but optional. A complete
> example
> may look like this::
>
> HKEY_CURRENT_USER\Software\Python\ExampleCorp\6C465E66
> (Default) = (value not set)
> DisplayName = "Distro 3"
> SupportUrl = "http://www.example.com/distro-3"
> Version = "3.0.12345.0"
> SysVersion = "3.6.0"
>
> InstallPath
> -----------
>
> Beneath the environment key, an ``InstallPath`` key must be created. This
> key is
> always named ``InstallPath``, and the default value must match
> ``sys.prefix``::
>
> HKEY_CURRENT_USER\Software\Python\ExampleCorp\3.6\InstallPath
> (Default) = "C:\ExampleCorpPy36"
>
> If a string value named ``ExecutablePath`` exists, it must be a path to the
> ``python.exe`` (or equivalent) executable. Otherwise, the interpreter
> executable
> is assumed to be called ``python.exe`` and exist in the directory referenced
> by
> the default value.
>
> If a string value named ``WindowedExecutablePath`` exists, it must be a path
> to
> the ``pythonw.exe`` (or equivalent) executable. Otherwise, the windowed
> interpreter executable is assumed to be called ``pythonw.exe`` and exist in
> the
> directory referenced by the default value.
>
> A complete example may look like::
>
> HKEY_CURRENT_USER\Software\Python\ExampleCorp\6C465E66\InstallPath
> (Default) = "C:\ExampleDistro30"
> ExecutablePath = "C:\ExampleDistro30\ex_python.exe"
> WindowedExecutablePath = "C:\ExampleDistro30\ex_pythonw.exe"
>
> Help
> ----
>
> Beneath the environment key, a ``Help`` key may be created. This key is
> always
> named ``Help`` if present and has no default value.
>
> Each subkey of ``Help`` specifies a documentation file, tool, or URL
> associated
> with the environment. The subkey may have any name, and the default value is
> a
> string appropriate for passing to ``os.startfile`` or equivalent.
>
> If a string value named ``DisplayName`` exists, it should be used to
> identify
> the help file to users. Otherwise, the key name should be used.
>
> A complete example may look like::
>
> HKEY_CURRENT_USER\Software\Python\ExampleCorp\6C465E66\Help
> Python\
> (Default) = "C:\ExampleDistro30\python36.chm"
> DisplayName = "Python Documentation"
> Extras\
> (Default) = "http://www.example.com/tutorial"
> DisplayName = "Example Distro Online Tutorial"
>
> Other Keys
> ----------
>
> Some other registry keys are used for defining or inferring search paths
> under
> certain conditions. A third-party installation is permitted to define these
> keys
> under their Company-Tag key, however, the interpreter must be modified and
> rebuilt in order to read these values. Alternatively, the interpreter may be
> modified to not use any registry keys for determining search paths. Making
> such
> changes is a decision for the third party; this PEP makes no recommendation
> either way.
>
> Copyright
> =========
>
> This document has been placed in the public domain.
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--
--Guido van Rossum (python.org/~guido)
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