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181 lines
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ReStructuredText
181 lines
7.2 KiB
ReStructuredText
:mod:`venv` --- Creation of virtual environments
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================================================
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.. module:: venv
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:synopsis: Creation of virtual environments.
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.. moduleauthor:: Vinay Sajip <vinay_sajip@yahoo.co.uk>
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.. sectionauthor:: Vinay Sajip <vinay_sajip@yahoo.co.uk>
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.. index:: pair: Environments; virtual
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.. versionadded:: 3.3
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**Source code:** :source:`Lib/venv.py`
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--------------
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The :mod:`venv` module provides support for creating lightweight "virtual
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environments" with their own site directories, optionally isolated from system
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site directories. Each virtual environment has its own Python binary (allowing
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creation of environments with various Python versions) and can have its own
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independent set of installed Python packages in its site directories.
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Creating virtual environments
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-----------------------------
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.. include:: /using/venv-create.inc
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.. _venv-def:
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.. note:: A virtual environment (also called a ``venv``) is a Python
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environment such that the Python interpreter, libraries and scripts
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installed into it are isolated from those installed in other virtual
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environments, and (by default) any libraries installed in a "system" Python,
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i.e. one which is installed as part of your operating system.
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A venv is a directory tree which contains Python executable files and
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other files which indicate that it is a venv.
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Common installation tools such as ``Distribute`` and ``pip`` work as
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expected with venvs - i.e. when a venv is active, they install Python
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packages into the venv without needing to be told to do so explicitly.
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Of course, you need to install them into the venv first: this could be
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done by running ``distribute_setup.py`` with the venv activated,
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followed by running ``easy_install pip``. Alternatively, you could download
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the source tarballs and run ``python setup.py install`` after unpacking,
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with the venv activated.
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When a venv is active (i.e. the venv's Python interpreter is running), the
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attributes :attr:`sys.prefix` and :attr:`sys.exec_prefix` point to the base
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directory of the venv, whereas :attr:`sys.base_prefix` and
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:attr:`sys.base_exec_prefix` point to the non-venv Python installation
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which was used to create the venv. If a venv is not active, then
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:attr:`sys.prefix` is the same as :attr:`sys.base_prefix` and
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:attr:`sys.exec_prefix` is the same as :attr:`sys.base_exec_prefix` (they
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all point to a non-venv Python installation).
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API
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---
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.. highlight:: python
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The high-level method described above makes use of a simple API which provides
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mechanisms for third-party virtual environment creators to customize environment
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creation according to their needs, the :class:`EnvBuilder` class.
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.. class:: EnvBuilder(system_site_packages=False, clear=False, symlinks=False, upgrade=False)
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The :class:`EnvBuilder` class accepts the following keyword arguments on
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instantiation:
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* ``system_site_packages`` -- a Boolean value indicating that the system Python
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site-packages should be available to the environment (defaults to ``False``).
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* ``clear`` -- a Boolean value which, if True, will delete any existing target
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directory instead of raising an exception (defaults to ``False``).
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* ``symlinks`` -- a Boolean value indicating whether to attempt to symlink the
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Python binary (and any necessary DLLs or other binaries,
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e.g. ``pythonw.exe``), rather than copying. Defaults to ``True`` on Linux and
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Unix systems, but ``False`` on Windows.
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* ``upgrade`` -- a Boolean value which, if True, will upgrade an existing
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environment with the running Python - for use when that Python has been
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upgraded in-place (defaults to ``False``).
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Creators of third-party virtual environment tools will be free to use the
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provided ``EnvBuilder`` class as a base class.
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The returned env-builder is an object which has a method, ``create``:
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.. method:: create(env_dir)
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This method takes as required argument the path (absolute or relative to
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the current directory) of the target directory which is to contain the
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virtual environment. The ``create`` method will either create the
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environment in the specified directory, or raise an appropriate
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exception.
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The ``create`` method of the ``EnvBuilder`` class illustrates the hooks
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available for subclass customization::
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def create(self, env_dir):
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"""
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Create a virtualized Python environment in a directory.
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env_dir is the target directory to create an environment in.
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"""
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env_dir = os.path.abspath(env_dir)
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context = self.create_directories(env_dir)
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self.create_configuration(context)
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self.setup_python(context)
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self.setup_scripts(context)
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self.post_setup(context)
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Each of the methods :meth:`create_directories`,
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:meth:`create_configuration`, :meth:`setup_python`,
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:meth:`setup_scripts` and :meth:`post_setup` can be overridden.
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.. method:: create_directories(env_dir)
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Creates the environment directory and all necessary directories, and
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returns a context object. This is just a holder for attributes (such as
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paths), for use by the other methods.
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.. method:: create_configuration(context)
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Creates the ``pyvenv.cfg`` configuration file in the environment.
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.. method:: setup_python(context)
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Creates a copy of the Python executable (and, under Windows, DLLs) in
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the environment.
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.. method:: setup_scripts(context)
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Installs activation scripts appropriate to the platform into the virtual
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environment.
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.. method:: post_setup(context)
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A placeholder method which can be overridden in third party
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implementations to pre-install packages in the virtual environment or
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perform other post-creation steps.
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In addition, :class:`EnvBuilder` provides this utility method that can be
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called from :meth:`setup_scripts` or :meth:`post_setup` in subclasses to
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assist in installing custom scripts into the virtual environment.
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.. method:: install_scripts(context, path)
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*path* is the path to a directory that should contain subdirectories
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"common", "posix", "nt", each containing scripts destined for the bin
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directory in the environment. The contents of "common" and the
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directory corresponding to :data:`os.name` are copied after some text
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replacement of placeholders:
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* ``__VENV_DIR__`` is replaced with the absolute path of the environment
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directory.
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* ``__VENV_NAME__`` is replaced with the environment name (final path
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segment of environment directory).
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* ``__VENV_BIN_NAME__`` is replaced with the name of the bin directory
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(either ``bin`` or ``Scripts``).
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* ``__VENV_PYTHON__`` is replaced with the absolute path of the
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environment's executable.
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There is also a module-level convenience function:
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.. function:: create(env_dir, system_site_packages=False, clear=False, symlinks=False)
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Create an :class:`EnvBuilder` with the given keyword arguments, and call its
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:meth:`~EnvBuilder.create` method with the *env_dir* argument.
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