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Edits from ncoghlan review.

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Carl Meyer 2012-05-24 15:46:52 -06:00
parent 2a01d82b09
commit 4162cd4583
1 changed files with 40 additions and 38 deletions
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pep-0405.txt
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@ -78,12 +78,13 @@ that signifies the presence of the standard library, and if none is
found, falling back to the build-time prefix hardcoded in the binary. found, falling back to the build-time prefix hardcoded in the binary.
This PEP proposes to add a new first step to this search. If a This PEP proposes to add a new first step to this search. If a
``pyvenv.cfg`` file is found either adjacent to the Python executable, ``pyvenv.cfg`` file is found either adjacent to the Python executable or
or one directory above it, this file is scanned for lines of the form one directory above it (if the executable is a symlink, it is not
``key = value``. If a ``home`` key is found, this signifies that the dereferenced), this file is scanned for lines of the form ``key =
Python binary belongs to a virtual environment, and the value of the value``. If a ``home`` key is found, this signifies that the Python
``home`` key is the directory containing the Python executable used to binary belongs to a virtual environment, and the value of the ``home``
create this virtual environment. key is the directory containing the Python executable used to create
this virtual environment.
In this case, prefix-finding continues as normal using the value of In this case, prefix-finding continues as normal using the value of
the ``home`` key as the effective Python binary location, which finds the ``home`` key as the effective Python binary location, which finds
@ -95,14 +96,16 @@ this value, while ``sys.prefix`` is set to the directory containing
prefix-finding continues normally, and ``sys.prefix`` will be equal to prefix-finding continues normally, and ``sys.prefix`` will be equal to
``sys.base_prefix``.) ``sys.base_prefix``.)
Also, ``sys.base_exec_prefix`` is added, and handled similarly with
regard to ``sys.exec_prefix``. (``sys.exec_prefix`` is the equivalent of
``sys.prefix``, but for platform-specific files; by default it has the
same value as ``sys.prefix``.)
The ``site`` and ``sysconfig`` standard-library modules are modified The ``site`` and ``sysconfig`` standard-library modules are modified
such that the standard library and header files are are found relative such that the standard library and header files are are found relative
to ``sys.base_prefix``, while site-package directories ("purelib" and to ``sys.base_prefix`` / ``sys.base_exec_prefix``, while site-package
"platlib", in ``sysconfig`` terms) are still found relative to directories ("purelib" and "platlib", in ``sysconfig`` terms) are still
``sys.prefix``. found relative to ``sys.prefix`` / ``sys.exec_prefix``.
(Also, ``sys.base_exec_prefix`` is added, and handled similarly with
regard to ``sys.exec_prefix``.)
Thus, a Python virtual environment in its simplest form would consist Thus, a Python virtual environment in its simplest form would consist
of nothing more than a copy or symlink of the Python binary of nothing more than a copy or symlink of the Python binary
@ -147,12 +150,12 @@ Running this command creates the target directory (creating any parent
directories that don't exist already) and places a ``pyvenv.cfg`` file directories that don't exist already) and places a ``pyvenv.cfg`` file
in it with a ``home`` key pointing to the Python installation the in it with a ``home`` key pointing to the Python installation the
command was run from. It also creates a ``bin/`` (or ``Scripts`` on command was run from. It also creates a ``bin/`` (or ``Scripts`` on
Windows) subdirectory containing a copy (or symlink) of the Windows) subdirectory containing a copy (or symlink) of the ``python3``
``python3`` executable, and the ``pysetup3`` script from the executable, and the ``pysetup3`` script from the ``packaging`` standard
``packaging`` standard library module (to facilitate easy installation library module (to facilitate easy installation of packages from PyPI
of packages from PyPI into the new virtualenv). And it creates an into the new venv). And it creates an (initially empty)
(initially empty) ``lib/pythonX.Y/site-packages`` (or ``lib/pythonX.Y/site-packages`` (or ``Lib\site-packages`` on Windows)
``Lib\site-packages`` on Windows) subdirectory. subdirectory.
If the target directory already exists an error will be raised, unless If the target directory already exists an error will be raised, unless
the ``--clear`` option was provided, in which case the target the ``--clear`` option was provided, in which case the target
@ -160,27 +163,29 @@ directory will be deleted and virtual environment creation will
proceed as usual. proceed as usual.
The created ``pyvenv.cfg`` file also includes the The created ``pyvenv.cfg`` file also includes the
``include-system-site-packages`` key, set to ``true`` if ``venv`` is ``include-system-site-packages`` key, set to ``true`` if ``pyvenv`` is
run with the ``--system-site-packages`` option, ``false`` by default. run with the ``--system-site-packages`` option, ``false`` by default.
Multiple paths can be given to ``pyvenv``, in which case an identical Multiple paths can be given to ``pyvenv``, in which case an identical
virtualenv will be created, according to the given options, at each venv will be created, according to the given options, at each
provided path. provided path.
The ``venv`` module also provides "shell activation scripts" for POSIX The ``venv`` module also places "shell activation scripts" for POSIX and
and Windows systems which simply add the virtual environment's ``bin`` Windows systems in the ``bin`` or ``Scripts`` directory of the
(or ``Scripts``) directory to the front of the user's shell PATH. venv. These scripts simply add the virtual environment's ``bin`` (or
This is not strictly necessary for use of a virtual environment (as an ``Scripts``) directory to the front of the user's shell PATH. This is
explicit path to the venv's python binary or scripts can just as well not strictly necessary for use of a virtual environment (as an explicit
be used), but it is convenient. path to the venv's python binary or scripts can just as well be used),
but it is convenient.
In order to allow ``pysetup`` and other Python package managers to In order to allow ``pysetup`` and other Python package managers to
install packages into the virtual environment the same way they would install packages into the virtual environment the same way they would
install into a normal Python installation, and avoid special-casing install into a normal Python installation, and avoid special-casing
virtual environments in ``sysconfig`` beyond using ``sys.site_prefix`` virtual environments in ``sysconfig`` beyond using ``sys.base_prefix``
in place of ``sys.prefix``, the internal virtual environment layout in place of ``sys.prefix`` where appropriate, the internal virtual
mimics the layout of the Python installation itself on each platform. environment layout mimics the layout of the Python installation itself
So a typical virtual environment layout on a POSIX system would be:: on each platform. So a typical virtual environment layout on a POSIX
system would be::
pyvenv.cfg pyvenv.cfg
bin/python3 bin/python3
@ -301,10 +306,9 @@ This PEP proposes a slightly different approach, though one with
essentially the same effect and the same set of advantages and essentially the same effect and the same set of advantages and
disadvantages. Rather than symlinking or copying include files into the disadvantages. Rather than symlinking or copying include files into the
venv, we simply modify the sysconfig schemes so that header files are venv, we simply modify the sysconfig schemes so that header files are
always looked for relative to ``base_prefix`` rather than always sought relative to ``base_prefix`` rather than ``prefix``. (We
``prefix``. (We also create an ``include/`` directory within the venv, also create an ``include/`` directory within the venv, so installers
so installers have somewhere to put include files installed within the have somewhere to put include files installed within the env).
env).
Better handling of include files in distutils/packaging and, by Better handling of include files in distutils/packaging and, by
extension, pyvenv, is an area that may deserve its own future PEP. For extension, pyvenv, is an area that may deserve its own future PEP. For
@ -507,10 +511,8 @@ Reference Implementation
======================== ========================
The reference implementation is found in `a clone of the CPython The reference implementation is found in `a clone of the CPython
Mercurial repository`_. To test it, build and install it (the virtual Mercurial repository`_. To test it, build and run ``bin/pyvenv
environment tool currently does not run from a source tree). From the /path/to/new/venv`` to create a virtual environment.
installed Python, run ``bin/pyvenv /path/to/new/virtualenv`` to create
a virtual environment.
.. _a clone of the CPython Mercurial repository: http://hg.python.org/sandbox/vsajip#venv .. _a clone of the CPython Mercurial repository: http://hg.python.org/sandbox/vsajip#venv