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.. _tools-and-scripts:
Additional Tools and Scripts
============================
pyvenv - Creating virtual environments
--------------------------------------
Creation of virtual environments is done by 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.
.. note:: A virtual environment (also called a ``venv``) is a Python
environment such that the Python interpreter, libraries and scripts
installed into it are isolated from those installed in other virtual
environments, and (by default) any libraries installed in a "system" Python,
i.e. one which is installed as part of your operating system.
A venv is a directory tree which contains Python executable files and
other files which indicate that it is a venv.
Common installation tools such as ``distribute`` and ``pip`` work as
expected with venvs - i.e. when a venv is active, they install Python
packages into the venv without needing to be told to do so explicitly.
When a venv is active (i.e. the venv's Python interpreter is running), the
attributes :attr:`sys.prefix` and :attr:`sys.exec_prefix` point to the base
directory of the venv, whereas :attr:`sys.base_prefix` and
:attr:`sys.base_exec_prefix` point to the non-venv Python installation
which was used to create the venv. If a venv is not active, then
:attr:`sys.prefix` is the same as :attr:`sys.base_prefix` and
:attr:`sys.exec_prefix` is the same as :attr:`sys.base_exec_prefix` (they
all point to a non-venv Python installation).
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