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PEP 582: Updates sysconfig scheme requirement (#3014)

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Kushal Das 2023-02-13 16:29:31 +01:00 committed by GitHub
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@ -97,15 +97,20 @@ works. For example, ``__pypackages__`` will be ignored if the ``-P`` option or
the ``PYTHONSAFEPATH`` environment variable is set.
In order to be recognised, the ``__pypackages__`` directory must be laid out
according to the "prefix" scheme in the sysconfig module. Specifically, either
or both of the ``purelib`` and ``platlib`` directories must be present, using
the following code to determine the locations of those directories::
according to a new ``localpackages`` scheme in the sysconfig module.
Specifically, both of the ``purelib`` and ``platlib`` directories must be
present, using the following code to determine the locations of those
directories::
scheme = sysconfig.get_preferred_scheme("prefix")
scheme = "localpackages"
purelib = sysconfig.get_path("purelib", scheme, vars={"base": "__pypackages__", "platbase": "__pypackages__"})
platlib = sysconfig.get_path("platlib", scheme, vars={"base": "__pypackages__", "platbase": "__pypackages__"})
These two locations will be added to ``sys.path``, other directories or files in the ``__pypackages__`` directory will be silently ignored.
These two locations will be added to ``sys.path``, other directories or
files in the ``__pypackages__`` directory will be silently ignored. The
paths will be based on Python versions.
.. note:: There is a possible option of having a separate new API, it is documented at `issue #3013 <https://github.com/python/peps/issues/3013>`_.
Example
@ -170,7 +175,7 @@ working directory is used.
In another example scenario, a trainer of a Python class can say "Today we are
going to learn how to use Twisted! To start, please checkout our example
project, go to that directory, and then run ``python3 -m pip install twisted``."
project, go to that directory, and then run a given command to install Twisted."
That will install Twisted into a directory separate from ``python3``. There's no
need to discuss virtual environments, global versus user installs, etc. as the
@ -266,21 +271,10 @@ As the intended use of the feature is to install 3rd party libraries in the new
directory, it is important that tools, particularly installers, understand how to
manage ``__pypackages__``.
To minimise transition costs, the PEP proposes a layout for the
``__pypackages__`` directory that is compatible with pip's ``--prefix`` option,
in the most common cases, so that in the absence of any dedicated mechanism,
``pip install --prefix __pypackages__`` should work. However, this is
considered a transitional measure only, and there is no guarantee that in
exceptional cases where a distributor has customised things or pip has
special-case handling, ``pip install --prefix`` might not work and installation
will need to be handled manually.
In the longer term, it is hoped that tools will introduce a dedicated
"pypackages" installation mode that *is* guaranteed to match the expected
layout in all cases, removing the need for interim approaches like
``--prefix``. However, the question of how best to support the
``__pypackages__`` layout is ultimately left to individual tool maintainers to
consider and decide on.
It is hoped that tools will introduce a dedicated "pypackages" installation
mode that *is* guaranteed to match the expected layout in all cases. However,
the question of how best to support the ``__pypackages__`` layout is ultimately
left to individual tool maintainers to consider and decide on.
Tools that locate packages without actually running Python code (IDEs, linters,
type checkers, etc.) would need updating to recognise ``__pypackages__``. In the