index.txt

virtualenv
==========

* `Discussion list <http://groups.google.com/group/python-virtualenv/>`_
* `Bugs <https://bugs.launchpad.net/virtualenv/>`_

.. contents::

Status and License
------------------

``virtualenv`` is a successor to `workingenv
<http://cheeseshop.python.org/pypi/workingenv.py>`_, and an extension
of `virtual-python
<http://peak.telecommunity.com/DevCenter/EasyInstall#creating-a-virtual-python>`_.

It is written by Ian Bicking, and sponsored by the `Open Planning
Project <http://topp.openplans.org>`_.  It is licensed under an
`MIT-style permissive license
<http://svn.colorstudy.com/virtualenv/trunk/docs/license.txt>`_.

You can install it with ``easy_install virtualenv``, or from the
`subversion repository
<http://svn.colorstudy.com/virtualenv/trunk#egg=virtualenv-dev>`_ with
``easy_install virtualenv==dev``.

What It Does
------------

``virtualenv`` is a tool to create isolated Python environments.

The basic problem being addressed is one of dependencies and versions,
and indirectly permissions.  Imagine you have an application that
needs version 1 of LibFoo, but another application requires version
2.  How can you use both these applications?  If you install
everything into ``/usr/lib/python2.4/site-packages`` (or whatever your
platform's standard location is), it's easy to end up in a situation
where you unintentionally upgrade an application that shouldn't be
upgraded.

Or more generally, what if you want to install an application *and
leave it be*?  If an application works, any change in its libraries or
the versions of those libraries can break the application.

Also, what if you can't install packages into the global
``site-packages`` directory?  For instance, on a shared host.

In all these cases, ``virtualenv`` can help you.  It creates an
environment that has its own installation directories, that doesn't
share libraries with other virtualenv environments (and optionally
doesn't use the globally installed libraries either).

The basic usage is::

    $ python virtualenv.py ENV

If you install it you can also just do ``virtualenv ENV``.

This creates ``ENV/lib/python2.4/site-packages`` (or
``ENV/lib/python2.5/site-packages`` on Python 2.5, etc), where any
libraries you install will go.  It also creates ``ENV/bin/python``,
which is a Python interpreter that uses this environment.  Anytime you
use that interpreter (including when a script has
``#!/path/to/ENV/bin/python`` in it) the libraries in that environment
will be used.  (**Note for Windows:** scripts and executables on
Windows go in ``ENV\Scripts\``; everywhere you see ``bin/`` replace it
with ``Scripts\``)

It also installs `Setuptools
<http://peak.telecommunity.com/DevCenter/setuptools>`_ for you, and if
you use ``ENV/bin/easy_install`` the packages will be installed into
the environment.

Creating Your Own Bootstrap Scripts
-----------------------------------

While this creates an environment, it doesn't put anything into the
environment.  Developers may find it useful to distribute a script
that sets up a particular environment, for example a script that
installs a particular web application.

To create a script like this, call
``virtualenv.create_bootstrap_script(extra_text)``, and write the
result to your new bootstrapping script.  Here's the documentation
from the docstring:

Creates a bootstrap script, which is like this script but with
extend_parser, adjust_options, and after_install hooks.

This returns a string that (written to disk of course) can be used
as a bootstrap script with your own customizations.  The script
will be the standard virtualenv.py script, with your extra text
added (your extra text should be Python code).

If you include these functions, they will be called:

``extend_parser(optparse_parser)``:
    You can add or remove options from the parser here.

``adjust_options(options, args)``:
    You can change options here, or change the args (if you accept
    different kinds of arguments, be sure you modify ``args`` so it is
    only ``[DEST_DIR]``).

``after_install(options, home_dir)``:

    After everything is installed, this function is called.  This
    is probably the function you are most likely to use.  An
    example would be::

        def after_install(options, home_dir):
            if sys.platform == 'win32':
                bin = 'Scripts'
            else:
                bin = 'bin'
            subprocess.call([join(home_dir, bin, 'easy_install'),
                             'MyPackage'])
            subprocess.call([join(home_dir, bin, 'my-package-script'),
                             'setup', home_dir])

    This example immediately installs a package, and runs a setup
    script from that package.

Bootstrap Example
~~~~~~~~~~~~~~~~~

Here's a more concrete example of how you could use this::

    import virtualenv, textwrap
    output = virtualenv.create_bootstrap_script(textwrap.dedent("""
    import os, subprocess
    def after_install(options, home_dir):
        etc = join(home_dir, 'etc')
        if not os.path.exists(etc):
            os.makedirs(etc)
        subprocess.call([join(home_dir, 'bin', 'easy_install'),
                         'BlogApplication'])
        subprocess.call([join(home_dir, 'bin', 'paster'),
                         'make-config', 'BlogApplication',
                         join(etc, 'blog.ini')])
        subprocess.call([join(home_dir, 'bin', 'paster'),
                         'setup-app', join(etc, 'blog.ini')])
    """))
    f = open('blog-bootstrap.py', 'w').write(output)

Another example is available `here
<https://svn.openplans.org/svn/fassembler/trunk/fassembler/create-venv-script.py>`_.

activate script
~~~~~~~~~~~~~~~

In a newly created virtualenv there will be a ``bin/activate`` shell
script, or a ``Scripts/activate.bat`` batch file on Windows.

On Posix systems you can do::

  $ source bin/activate

This will change your ``$PATH`` to point to the virtualenv ``bin/``
directory, and update your prompt.  Unlike workingenv, this is all it
does; it's a convenience.  But if you use the complete path like
``/path/to/env/bin/python script.py`` you do not need to activate the
environment first.  You have to use ``source`` because it changes the
environment in-place.  After activating an environment you can use the
function ``deactivate`` to undo the changes.

On Windows you just do::

  > \path\to\env\bin\activate.bat

And use ``deactivate.bat`` to undo the changes.

The ``--no-site-packages`` Option
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you build with ``virtualenv --no-site-packages ENV`` it will *not*
inherit any packages from ``/usr/lib/python2.5/site-packages`` (or
wherever your global site-packages directory is).  This can be used if
you don't have control over site-packages and don't want to depend on
the packages there, or you just want more isolation from the global
system.

Using Virtualenv without ``bin/python``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sometimes you can't or don't want to use the Python interpreter
created by the virtualenv.  For instance, in a `mod_python
<http://www.modpython.org/>`_ or `mod_wsgi <http://www.modwsgi.org/>`_
environment, there is only one interpreter.

Luckily, it's easy.  You must use the custom Python interpreter to
*install* libraries.  But to *use* libraries, you just have to be sure
the path is correct.  A script is available to correct the path.  You
can setup the environment like::

    activate_this = '/path/to/env/bin/activate_this.py'
    execfile(activate_this, dict(__file__=activate_this))

This will change ``sys.path`` and even change ``sys.prefix``, but also
allow you to use an existing interpreter.  Items in your environment
will show up first on ``sys.path``, before global items.  However,
this cannot undo the activation of other environments, or modules that
have been imported.  You shouldn't try to, for instance, activate an
environment before a web request; you should activate *one*
environment as early as possible, and not do it again in that process.

Making Environments Relocatable
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Note: this option is somewhat experimental, and there are probably
caveats that have not yet been identified.  Also this does not
currently work on Windows.

Normally environments are tied to a specific path.  That means that
you cannot move an environment around or copy it to another computer.
You can fix up an environment to make it relocatable with the
command::

    $ virtualenv --relocatable ENV

This will make some of the files created by setuptools use relative
paths, and will change all the scripts to use ``activate_this.py``
instead of using the location of the Python interpreter to select the
environment.

**Note:** you must run this after you've installed *any* packages into
the environment.  If you make an environment relocatable, then
install a new package, you must run ``virtualenv --relocatable``
again.

Also, this **does not make your packages cross-platform**.  You can
move the directory around, but it can only be used on other similar
computers.  Some known environmental differences that can cause
incompatibilities: a different version of Python, when one platform
uses UCS2 for its internal unicode representation and another uses
UCS4 (a compile-time option), obvious platform changes like Windows
vs. Linux, or Intel vs. ARM, and if you have libraries that bind to C
libraries on the system, if those C libraries are located somewhere
different (either different versions, or a different filesystem
layout).

Currently the ``--no-site-packages`` option will not be honored if you
use this on an environment.

Compare & Contrast with Alternatives
------------------------------------

There are several alternatives that create isolated environments:

* ``workingenv`` (which I do not suggest you use anymore) is the
  predecessor to this library.  It used the main Python interpreter,
  but relied on setting ``$PYTHONPATH`` to activate the environment.
  This causes problems when running Python scripts that aren't part of
  the environment (e.g., a globally installed ``hg`` or ``bzr``).  It
  also conflicted a lot with Setuptools.

* `virtual-python
  <http://peak.telecommunity.com/DevCenter/EasyInstall#creating-a-virtual-python>`_
  is also a predecessor to this library.  It uses only symlinks, so it
  couldn't work on Windows.  It also symlinks over the *entire*
  standard library and global ``site-packages``.  As a result, it
  won't see new additions to the global ``site-packages``.

  This script only symlinks a small portion of the standard library
  into the environment, and so on Windows it is feasible to simply
  copy these files over.  Also, it creates a new/empty
  ``site-packages`` and also adds the global ``site-packages`` to the
  path, so updates are tracked separately.  This script also installs
  Setuptools automatically, saving a step and avoiding the need for
  network access.

* `zc.buildout <http://pypi.python.org/pypi/zc.buildout>`_ doesn't
  create an isolated Python environment in the same style, but
  achieves similar results through a declarative config file that sets
  up scripts with very particular packages.  As a declarative system,
  it is somewhat easier to repeat and manage, but more difficult to
  experiment with.  ``zc.buildout`` includes the ability to setup
  non-Python systems (e.g., a database server or an Apache instance).

I *strongly* recommend anyone doing application development or
deployment use one of these tools.

Other Documentation and Links
-----------------------------

* James Gardner has written a tutorial on using `virtualenv with
  Pylons
  <http://wiki.pylonshq.com/display/pylonscookbook/Using+a+Virtualenv+Sandbox>`_.

* `Blog announcement
  <http://blog.ianbicking.org/2007/10/10/workingenv-is-dead-long-live-virtualenv/>`_.

* Doug Hellmann wrote a description of his `command-line work flow
  using virtualenv (virtualenvwrapper)
  <http://www.doughellmann.com/articles/CompletelyDifferent-2008-05-virtualenvwrapper/index.html>`_
  including some handy scripts to make working with multiple
  environments easier.  He also wrote `an example of using virtualenv
  to try IPython
  <http://www.doughellmann.com/articles/CompletelyDifferent-2008-02-ipython-and-virtualenv/index.html>`_.

* Chris Perkins created a `showmedo video including virtualenv
  <http://showmedo.com/videos/video?name=2910000&fromSeriesID=291>`_.

* `Using virtualenv with mod_wsgi
  <http://code.google.com/p/modwsgi/wiki/VirtualEnvironments>`_.

Changes & News
--------------

1.3.3
~~~~~

* Use Windows newlines in ``activate.bat``, which has been reported to help
  when using non-ASCII directory names.

* Fixed compatibility with Jython 2.5b1.

* Added a function ``virtualenv.install_python`` for more fine-grained
  access to what ``virtualenv.create_environment`` does.

* Fix `a problem <https://bugs.launchpad.net/virtualenv/+bug/241581>`_
  with Windows and paths that contain spaces.

* If ``/path/to/env/.pydistutils.cfg`` exists (or
  ``/path/to/env/pydistutils.cfg`` on Windows systems) then ignore
  ``~/.pydistutils.cfg`` and use that other file instead.

* Fix ` a problem
  <https://bugs.launchpad.net/virtualenv/+bug/340050>`_ picking up
  some ``.so`` libraries in ``/usr/local``.

1.3.2
~~~~~

* Remove the ``[install] prefix = ...`` setting from the virtualenv
  ``distutils.cfg`` -- this has been causing problems for a lot of
  people, in rather obscure ways.

* If you use a `boot script`_ it will attempt to import ``virtualenv``
  and find a pre-downloaded Setuptools egg using that.

.. _boot script: `Creating Your Own Bootstrap Scripts`_

* Added platform-specific paths, like ``/usr/lib/pythonX.Y/plat-linux2``

1.3.1
~~~~~

* Real Python 2.6 compatibility.  Backported the Python 2.6 updates to
  ``site.py``, including `user directories
  <http://docs.python.org/dev/whatsnew/2.6.html#pep-370-per-user-site-packages-directory>`_
  (this means older versions of Python will support user directories,
  whether intended or not).

* Always set ``[install] prefix`` in ``distutils.cfg`` -- previously
  on some platforms where a system-wide ``distutils.cfg`` was present
  with a ``prefix`` setting, packages would be installed globally
  (usually in ``/usr/local/lib/pythonX.Y/site-packages``).

* Sometimes Cygwin seems to leave ``.exe`` off ``sys.executable``; a
  workaround is added.

* Fix ``--python`` option.

* Fixed handling of Jython environments that use a
  jython-complete.jar.

1.3
~~~

* Update to Setuptools 0.6c9
* Added an option ``virtualenv --relocatable EXISTING_ENV``, which
  will make an existing environment "relocatable" -- the paths will
  not be absolute in scripts, ``.egg-info`` and ``.pth`` files.  This
  may assist in building environments that can be moved and copied.
  You have to run this *after* any new packages installed.
* Added ``bin/activate_this.py``, a file you can use like
  ``execfile("path_to/activate_this.py",
  dict(__file__="path_to/activate_this.py"))`` -- this will activate
  the environment in place, similar to what `the mod_wsgi example
  does <http://code.google.com/p/modwsgi/wiki/VirtualEnvironments>`_.
* For Mac framework builds of Python, the site-packages directory
  ``/Library/Python/X.Y/site-packages`` is added to ``sys.path``, from
  Andrea Rech.
* Some platform-specific modules in Macs are added to the path now
  (``plat-darwin/``, ``plat-mac/``, ``plat-mac/lib-scriptpackages``),
  from Andrea Rech.
* Fixed a small Bashism in the ``bin/activate`` shell script.
* Added ``__future__`` to the list of required modules, for Python
  2.3.  You'll still need to backport your own ``subprocess`` module.
* Fixed the ``__classpath__`` entry in Jython's ``sys.path`` taking
  precedent over virtualenv's libs.

1.2
~~~

* Added a ``--python`` option to select the Python interpreter.
* Add ``warnings`` to the modules copied over, for Python 2.6 support.
* Add ``sets`` to the module copied over for Python 2.3 (though Python
  2.3 still probably doesn't work).

1.1.1
~~~~~

* Added support for Jython 2.5.

1.1
~~~

* Added support for Python 2.6.
* Fix a problem with missing ``DLLs/zlib.pyd`` on Windows.  Create
* ``bin/python`` (or ``bin/python.exe``) even when you run virtualenv
  with an interpreter named, e.g., ``python2.4``
* Fix MacPorts Python
* Added --unzip-setuptools option
* Update to Setuptools 0.6c8
* If the current directory is not writable, run ez_setup.py in ``/tmp``
* Copy or symlink over the ``include`` directory so that packages will
  more consistently compile.

1.0
~~~

* Fix build on systems that use ``/usr/lib64``, distinct from
  ``/usr/lib`` (specifically CentOS x64).
* Fixed bug in ``--clear``.
* Fixed typos in ``deactivate.bat``.
* Preserve ``$PYTHONPATH`` when calling subprocesses.

0.9.2
~~~~~

* Fix include dir copying on Windows (makes compiling possible).
* Include the main ``lib-tk`` in the path.
* Patch ``distutils.sysconfig``: ``get_python_inc`` and
  ``get_python_lib`` to point to the global locations.
* Install ``distutils.cfg`` before Setuptools, so that system
  customizations of ``distutils.cfg`` won't effect the installation.
* Add ``bin/pythonX.Y`` to the virtualenv (in addition to
  ``bin/python``).
* Fixed an issue with Mac Framework Python builds, and absolute paths
  (from Ronald Oussoren).

0.9.1
~~~~~

* Improve ability to create a virtualenv from inside a virtualenv.
* Fix a little bug in ``bin/activate``.
* Actually get ``distutils.cfg`` to work reliably.

0.9
~~~

* Added ``lib-dynload`` and ``config`` to things that need to be
  copied over in an environment.
* Copy over or symlink the ``include`` directory, so that you can
  build packages that need the C headers.
* Include a ``distutils`` package, so you can locally update
  ``distutils.cfg`` (in ``lib/pythonX.Y/distutils/distutils.cfg``).
* Better avoid downloading Setuptools, and hitting PyPI on environment
  creation. 
* Fix a problem creating a ``lib64/`` directory.
* Should work on MacOSX Framework builds (the default Python
  installations on Mac).  Thanks to Ronald Oussoren.

0.8.4
~~~~~

* Windows installs would sometimes give errors about ``sys.prefix`` that
  were inaccurate.
* Slightly prettier output.

0.8.3
~~~~~

* Added support for Windows.

0.8.2
~~~~~

* Give a better warning if you are on an unsupported platform (Mac
  Framework Pythons, and Windows).
* Give error about running while inside a workingenv.
* Give better error message about Python 2.3.

0.8.1
~~~~~

Fixed packaging of the library.

0.8
~~~

Initial release.  Everything is changed and new!