:mod:`venv` --- Creation of virtual environments ================================================ .. module:: venv :synopsis: Creation of virtual environments. .. moduleauthor:: Vinay Sajip .. sectionauthor:: Vinay Sajip .. 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 --- 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 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. The returned env-builder is an object which has a method, ``create``, which 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. Creators of third-party virtual environment tools will be free to use the provided ``EnvBuilder`` class as a base class. .. highlight:: python The ``venv`` module will also provide a module-level function as a convenience:: def create(env_dir, system_site_packages=False, clear=False, symlinks=False): builder = EnvBuilder( system_site_packages=system_site_packages, clear=clear, symlinks=symlinks) builder.create(env_dir) 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 ``create_directories``, ``create_configuration``, ``setup_python``, ``setup_scripts`` and ``post_setup`` can be overridden. The functions of these methods are: * ``create_directories`` - 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. * ``create_configuration`` - creates the ``pyvenv.cfg`` configuration file in the environment. * ``setup_python`` - creates a copy of the Python executable (and, under Windows, DLLs) in the environment. * ``setup_scripts`` - Installs activation scripts appropriate to the platform into the virtual environment. * ``post_setup`` - 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, ``EnvBuilder`` provides an ``install_scripts`` utility method that can be called from ``setup_scripts`` or ``post_setup`` in subclasses to assist in installing custom scripts into the virtual environment. The method accepts as arguments the context object (see above) and a path to a directory. The directory 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 ``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.