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diff --git a/Doc/library/venv.rst b/Doc/library/venv.rst new file mode 100644 index 0000000..e5c91e4 --- /dev/null +++ b/Doc/library/venv.rst @@ -0,0 +1,199 @@ +:mod:`venv` --- Creation of virtual environments +================================================ + +.. module:: venv + :synopsis: Creation of virtual environments. +.. moduleauthor:: Vinay Sajip <vinay_sajip@yahoo.co.uk> +.. sectionauthor:: Vinay Sajip <vinay_sajip@yahoo.co.uk> + + +.. index:: pair: Environments; virtual + +.. versionadded:: 3.3 + +**Source code:** :source:`Lib/venv.py` + +-------------- + +The :mod:`venv` module provides support for creating lightweight "virtual +environments" with their own site directories, optionally isolated from system +site directories. Each virtual environment has its own Python binary (allowing +creation of environments with various Python versions) and can have its own +independent set of installed Python packages in its site directories. + + +Creating virtual environments +----------------------------- + +Creation of virtual environments is simplest executing the ``pyvenv`` script:: + + pyvenv /path/to/new/virtual/environment + +Running this command creates the target directory (creating any parent +directories that don't exist already) and places a ``pyvenv.cfg`` file in it +with a ``home`` key pointing to the Python installation the command was run +from. It also creates a ``bin`` (or ``Scripts`` on Windows) subdirectory +containing a copy of the ``python`` binary (or binaries, in the case of +Windows). It also creates an (initially empty) ``lib/pythonX.Y/site-packages`` +subdirectory (on Windows, this is ``Lib\site-packages``). + +.. highlight:: none + +On Windows, you may have to invoke the ``pyvenv`` script as follows, if you +don't have the relevant PATH and PATHEXT settings:: + + c:\Temp>c:\Python33\python c:\Python33\Tools\Scripts\pyvenv.py myenv + +or equivalently:: + + c:\Temp>c:\Python33\python -m venv myenv + +The command, if run with ``-h``, will show the available options:: + + usage: pyvenv [-h] [--system-site-packages] [--symlink] [--clear] + [--upgrade] ENV_DIR [ENV_DIR ...] + + Creates virtual Python environments in one or more target directories. + + positional arguments: + ENV_DIR A directory to create the environment in. + + optional arguments: + -h, --help show this help message and exit + --system-site-packages Give access to the global site-packages dir to the + virtual environment. + --symlink Attempt to symlink rather than copy. + --clear Delete the environment directory if it already exists. + If not specified and the directory exists, an error is + raised. + --upgrade Upgrade the environment directory to use this version + of Python, assuming Python has been upgraded in-place. + +If the target directory already exists an error will be raised, unless the +``--clear`` or ``--upgrade`` option was provided. + +The created ``pyvenv.cfg`` file also includes the +``include-system-site-packages`` key, set to ``true`` if ``venv`` is run with +the ``--system-site-packages`` option, ``false`` otherwise. + +Multiple paths can be given to ``pyvenv``, in which case an identical virtualenv +will be created, according to the given options, at each provided path. + + +API +--- + +.. highlight:: python + +The high-level method described above makes use of a simple API which provides +mechanisms for third-party virtual environment creators to customize environment +creation according to their needs, the :class:`EnvBuilder` class. + +.. class:: EnvBuilder(system_site_packages=False, clear=False, symlinks=False, upgrade=False) + + The :class:`EnvBuilder` class accepts the following keyword arguments on + instantiation: + + * ``system_site_packages`` -- a Boolean value indicating that the system Python + site-packages should be available to the environment (defaults to ``False``). + + * ``clear`` -- a Boolean value which, if True, will delete any existing target + directory instead of raising an exception (defaults to ``False``). + + * ``symlinks`` -- a Boolean value indicating whether to attempt to symlink the + Python binary (and any necessary DLLs or other binaries, + e.g. ``pythonw.exe``), rather than copying. Defaults to ``True`` on Linux and + Unix systems, but ``False`` on Windows and Mac OS X. + + .. XXX it also takes "upgrade"! + + + Creators of third-party virtual environment tools will be free to use the + provided ``EnvBuilder`` class as a base class. + + The returned env-builder is an object which has a method, ``create``: + + .. method:: create(env_dir) + + This method takes as required argument the path (absolute or relative to + the current directory) of the target directory which is to contain the + virtual environment. The ``create`` method will either create the + environment in the specified directory, or raise an appropriate + exception. + + The ``create`` method of the ``EnvBuilder`` class illustrates the hooks + available for subclass customization:: + + def create(self, env_dir): + """ + Create a virtualized Python environment in a directory. + env_dir is the target directory to create an environment in. + """ + env_dir = os.path.abspath(env_dir) + context = self.create_directories(env_dir) + self.create_configuration(context) + self.setup_python(context) + self.setup_scripts(context) + self.post_setup(context) + + Each of the methods :meth:`create_directories`, + :meth:`create_configuration`, :meth:`setup_python`, + :meth:`setup_scripts` and :meth:`post_setup` can be overridden. + + .. method:: create_directories(env_dir) + + Creates the environment directory and all necessary directories, and + returns a context object. This is just a holder for attributes (such as + paths), for use by the other methods. + + .. method:: create_configuration(context) + + Creates the ``pyvenv.cfg`` configuration file in the environment. + + .. method:: setup_python(context) + + Creates a copy of the Python executable (and, under Windows, DLLs) in + the environment. + + .. method:: setup_scripts(context) + + Installs activation scripts appropriate to the platform into the virtual + environment. + + .. method:: post_setup(context) + + A placeholder method which can be overridden in third party + implementations to pre-install packages in the virtual environment or + perform other post-creation steps. + + In addition, :class:`EnvBuilder` provides this utility method that can be + called from :meth:`setup_scripts` or :meth:`post_setup` in subclasses to + assist in installing custom scripts into the virtual environment. + + .. method:: install_scripts(context, path) + + *path* is the path to a directory that should contain subdirectories + "common", "posix", "nt", each containing scripts destined for the bin + directory in the environment. The contents of "common" and the + directory corresponding to :data:`os.name` are copied after some text + replacement of placeholders: + + * ``__VENV_DIR__`` is replaced with the absolute path of the environment + directory. + + * ``__VENV_NAME__`` is replaced with the environment name (final path + segment of environment directory). + + * ``__VENV_BIN_NAME__`` is replaced with the name of the bin directory + (either ``bin`` or ``Scripts``). + + * ``__VENV_PYTHON__`` is replaced with the absolute path of the + environment's executable. + + +There is also a module-level convenience function: + +.. function:: create(env_dir, system_site_packages=False, clear=False, symlinks=False) + + Create an :class:`EnvBuilder` with the given keyword arguments, and call its + :meth:`~EnvBuilder.create` method with the *env_dir* argument. |