bootstrap/virtualenv/docs/userguide.rst - depot_tools - Git at Google

 User Guide
 ==========


 Usage
 -----

 Virtualenv has one basic command::

     $ virtualenv ENV

 Where ``ENV`` is a directory to place the new virtual environment. It has
 a number of usual effects (modifiable by many :ref:`options`):

  - :file:`ENV/lib/` and :file:`ENV/include/` are created, containing supporting
    library files for a new virtualenv python. Packages installed in this
    environment will live under :file:`ENV/lib/pythonX.X/site-packages/`.

  - :file:`ENV/bin` is created, where executables live - noticeably a new
    :command:`python`. Thus running a script with ``#! /path/to/ENV/bin/python``
    would run that script under this virtualenv's python.

  - The crucial packages pip_ and setuptools_ are installed, which allow other
    packages to be easily installed to the environment. This associated pip
    can be run from :file:`ENV/bin/pip`.

 The python in your new virtualenv is effectively isolated from the python that
 was used to create it.

 .. _pip: https://pypi.python.org/pypi/pip
 .. _setuptools: https://pypi.python.org/pypi/setuptools


 .. _activate:

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

 In a newly created virtualenv there will also be a :command:`activate` shell
 script. For Windows systems, activation scripts are provided for
 the Command Prompt and Powershell.

 On Posix systems, this resides in :file:`/ENV/bin/`, so you can run::

     $ source bin/activate

 For some shells (e.g. the original Bourne Shell) you may need to use the
 :command:`.` command, when :command:`source` does not exist.

 This will change your ``$PATH`` so its first entry is the virtualenv's
 ``bin/`` directory. (You have to use ``source`` because it changes your
 shell environment in-place.) This is all it does; it's purely a
 convenience. If you directly run a script or the python interpreter
 from the virtualenv's ``bin/`` directory (e.g. ``path/to/ENV/bin/pip``
 or ``/path/to/ENV/bin/python-script.py``) there's no need for
 activation.

 The ``activate`` script will also modify your shell prompt to indicate
 which environment is currently active. To disable this behaviour, see
 :envvar:`VIRTUAL_ENV_DISABLE_PROMPT`.

 To undo these changes to your path (and prompt), just run::

     $ deactivate

 On Windows, the equivalent `activate` script is in the ``Scripts`` folder::

     > \path\to\env\Scripts\activate

 And type ``deactivate`` to undo the changes.

 Based on your active shell (CMD.exe or Powershell.exe), Windows will use
 either activate.bat or activate.ps1 (as appropriate) to activate the
 virtual environment. If using Powershell, see the notes about code signing
 below.

 .. note::

     If using Powershell, the ``activate`` script is subject to the
     `execution policies`_ on the system. By default on Windows 7, the system's
     excution policy is set to ``Restricted``, meaning no scripts like the
     ``activate`` script are allowed to be executed. But that can't stop us
     from changing that slightly to allow it to be executed.

     In order to use the script, you can relax your system's execution
     policy to ``AllSigned``, meaning all scripts on the system must be
     digitally signed to be executed. Since the virtualenv activation
     script is signed by one of the authors (Jannis Leidel) this level of
     the execution policy suffices. As an administrator run::

         PS C:\> Set-ExecutionPolicy AllSigned

     Then you'll be asked to trust the signer, when executing the script.
     You will be prompted with the following::

         PS C:\> virtualenv .\foo
         New python executable in C:\foo\Scripts\python.exe
         Installing setuptools................done.
         Installing pip...................done.
         PS C:\> .\foo\scripts\activate

         Do you want to run software from this untrusted publisher?
         File C:\foo\scripts\activate.ps1 is published by E=jannis@leidel.info,
         CN=Jannis Leidel, L=Berlin, S=Berlin, C=DE, Description=581796-Gh7xfJxkxQSIO4E0
         and is not trusted on your system. Only run scripts from trusted publishers.
         [V] Never run  [D] Do not run  [R] Run once  [A] Always run  [?] Help
         (default is "D"):A
         (foo) PS C:\>

     If you select ``[A] Always Run``, the certificate will be added to the
     Trusted Publishers of your user account, and will be trusted in this
     user's context henceforth. If you select ``[R] Run Once``, the script will
     be run, but you will be prometed on a subsequent invocation. Advanced users
     can add the signer's certificate to the Trusted Publishers of the Computer
     account to apply to all users (though this technique is out of scope of this
     document).

     Alternatively, you may relax the system execution policy to allow running
     of local scripts without verifying the code signature using the following::

         PS C:\> Set-ExecutionPolicy RemoteSigned

     Since the ``activate.ps1`` script is generated locally for each virtualenv,
     it is not considered a remote script and can then be executed.

 .. _`execution policies`: http://technet.microsoft.com/en-us/library/dd347641.aspx

 The :option:`--system-site-packages` Option
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 If you build with ``virtualenv --system-site-packages ENV``, your virtual
 environment will inherit packages from ``/usr/lib/python2.7/site-packages``
 (or wherever your global site-packages directory is).

 This can be used if you have control over the global site-packages directory,
 and you want to depend on the packages there. If you want isolation from the
 global system, do not use this flag.

 Windows Notes
 ~~~~~~~~~~~~~

 Some paths within the virtualenv are slightly different on Windows: scripts and
 executables on Windows go in ``ENV\Scripts\`` instead of ``ENV/bin/`` and
 libraries go in ``ENV\Lib\`` rather than ``ENV/lib/``.

 To create a virtualenv under a path with spaces in it on Windows, you'll need
 the `win32api <http://sourceforge.net/projects/pywin32/>`_ library installed.


 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, global items will
 always be accessible (as if the :option:`--system-site-packages` flag had been
 used in creating the environment, whether it was or not). Also, 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.

 .. warning::

     The ``--relocatable`` option currently has a number of issues,
     and is not guaranteed to work in all circumstances. It is possible
     that the option will be deprecated in a future version of ``virtualenv``.

 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:** scripts which have been made relocatable will only work if
 the virtualenv is activated, specifically the python executable from
 the virtualenv must be the first one on the system PATH. Also note that
 the activate scripts are not currently made relocatable by
 ``virtualenv --relocatable``.

 **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).

 If you use this flag to create an environment, currently, the
 :option:`--system-site-packages` option will be implied.

 The :option:`--extra-search-dir` option
 ---------------------------------------

 This option allows you to provide your own versions of setuptools and/or
 pip to use instead of the embedded versions that come with virtualenv.

 To use this feature, pass one or more ``--extra-search-dir`` options to
 virtualenv like this::

     $ virtualenv --extra-search-dir=/path/to/distributions ENV

 The ``/path/to/distributions`` path should point to a directory that contains
 setuptools and/or pip wheels.

 virtualenv will look for wheels in the specified directories, but will use
 pip's standard algorithm for selecting the wheel to install, which looks for
 the latest compatible wheel.

 As well as the extra directories, the search order includes:

 #. The ``virtualenv_support`` directory relative to virtualenv.py
 #. The directory where virtualenv.py is located.
 #. The current directory.

 If no satisfactory local distributions are found, virtualenv will
 fail. Virtualenv will never download packages.
	User Guide
	==========


	Usage
	-----

	Virtualenv has one basic command::

	$ virtualenv ENV

	Where ``ENV`` is a directory to place the new virtual environment. It has
	a number of usual effects (modifiable by many :ref:`options`):

	- :file:`ENV/lib/` and :file:`ENV/include/` are created, containing supporting
	library files for a new virtualenv python. Packages installed in this
	environment will live under :file:`ENV/lib/pythonX.X/site-packages/`.

	- :file:`ENV/bin` is created, where executables live - noticeably a new
	:command:`python`. Thus running a script with ``#! /path/to/ENV/bin/python``
	would run that script under this virtualenv's python.

	- The crucial packages pip_ and setuptools_ are installed, which allow other
	packages to be easily installed to the environment. This associated pip
	can be run from :file:`ENV/bin/pip`.

	The python in your new virtualenv is effectively isolated from the python that
	was used to create it.

	.. _pip: https://pypi.python.org/pypi/pip
	.. _setuptools: https://pypi.python.org/pypi/setuptools


	.. _activate:

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

	In a newly created virtualenv there will also be a :command:`activate` shell
	script. For Windows systems, activation scripts are provided for
	the Command Prompt and Powershell.

	On Posix systems, this resides in :file:`/ENV/bin/`, so you can run::

	$ source bin/activate

	For some shells (e.g. the original Bourne Shell) you may need to use the
	:command:`.` command, when :command:`source` does not exist.

	This will change your ``$PATH`` so its first entry is the virtualenv's
	``bin/`` directory. (You have to use ``source`` because it changes your
	shell environment in-place.) This is all it does; it's purely a
	convenience. If you directly run a script or the python interpreter
	from the virtualenv's ``bin/`` directory (e.g. ``path/to/ENV/bin/pip``
	or ``/path/to/ENV/bin/python-script.py``) there's no need for
	activation.

	The ``activate`` script will also modify your shell prompt to indicate
	which environment is currently active. To disable this behaviour, see
	:envvar:`VIRTUAL_ENV_DISABLE_PROMPT`.

	To undo these changes to your path (and prompt), just run::

	$ deactivate

	On Windows, the equivalent `activate` script is in the ``Scripts`` folder::

	> \path\to\env\Scripts\activate

	And type ``deactivate`` to undo the changes.

	Based on your active shell (CMD.exe or Powershell.exe), Windows will use
	either activate.bat or activate.ps1 (as appropriate) to activate the
	virtual environment. If using Powershell, see the notes about code signing
	below.

	.. note::

	If using Powershell, the ``activate`` script is subject to the
	`execution policies`_ on the system. By default on Windows 7, the system's
	excution policy is set to ``Restricted``, meaning no scripts like the
	``activate`` script are allowed to be executed. But that can't stop us
	from changing that slightly to allow it to be executed.

	In order to use the script, you can relax your system's execution
	policy to ``AllSigned``, meaning all scripts on the system must be
	digitally signed to be executed. Since the virtualenv activation
	script is signed by one of the authors (Jannis Leidel) this level of
	the execution policy suffices. As an administrator run::

	PS C:\> Set-ExecutionPolicy AllSigned

	Then you'll be asked to trust the signer, when executing the script.
	You will be prompted with the following::

	PS C:\> virtualenv .\foo
	New python executable in C:\foo\Scripts\python.exe
	Installing setuptools................done.
	Installing pip...................done.
	PS C:\> .\foo\scripts\activate

	Do you want to run software from this untrusted publisher?
	File C:\foo\scripts\activate.ps1 is published by E=jannis@leidel.info,
	CN=Jannis Leidel, L=Berlin, S=Berlin, C=DE, Description=581796-Gh7xfJxkxQSIO4E0
	and is not trusted on your system. Only run scripts from trusted publishers.
	[V] Never run [D] Do not run [R] Run once [A] Always run [?] Help
	(default is "D"):A
	(foo) PS C:\>

	If you select ``[A] Always Run``, the certificate will be added to the
	Trusted Publishers of your user account, and will be trusted in this
	user's context henceforth. If you select ``[R] Run Once``, the script will
	be run, but you will be prometed on a subsequent invocation. Advanced users
	can add the signer's certificate to the Trusted Publishers of the Computer
	account to apply to all users (though this technique is out of scope of this
	document).

	Alternatively, you may relax the system execution policy to allow running
	of local scripts without verifying the code signature using the following::

	PS C:\> Set-ExecutionPolicy RemoteSigned

	Since the ``activate.ps1`` script is generated locally for each virtualenv,
	it is not considered a remote script and can then be executed.

	.. _`execution policies`: http://technet.microsoft.com/en-us/library/dd347641.aspx

	The :option:`--system-site-packages` Option
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	If you build with ``virtualenv --system-site-packages ENV``, your virtual
	environment will inherit packages from ``/usr/lib/python2.7/site-packages``
	(or wherever your global site-packages directory is).

	This can be used if you have control over the global site-packages directory,
	and you want to depend on the packages there. If you want isolation from the
	global system, do not use this flag.

	Windows Notes
	~~~~~~~~~~~~~

	Some paths within the virtualenv are slightly different on Windows: scripts and
	executables on Windows go in ``ENV\Scripts\`` instead of ``ENV/bin/`` and
	libraries go in ``ENV\Lib\`` rather than ``ENV/lib/``.

	To create a virtualenv under a path with spaces in it on Windows, you'll need
	the `win32api <http://sourceforge.net/projects/pywin32/>`_ library installed.


	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, global items will
	always be accessible (as if the :option:`--system-site-packages` flag had been
	used in creating the environment, whether it was or not). Also, 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.

	.. warning::

	The ``--relocatable`` option currently has a number of issues,
	and is not guaranteed to work in all circumstances. It is possible
	that the option will be deprecated in a future version of ``virtualenv``.

	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: scripts which have been made relocatable will only work if
	the virtualenv is activated, specifically the python executable from
	the virtualenv must be the first one on the system PATH. Also note that
	the activate scripts are not currently made relocatable by
	``virtualenv --relocatable``.

	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).

	If you use this flag to create an environment, currently, the
	:option:`--system-site-packages` option will be implied.

	The :option:`--extra-search-dir` option
	---------------------------------------

	This option allows you to provide your own versions of setuptools and/or
	pip to use instead of the embedded versions that come with virtualenv.

	To use this feature, pass one or more ``--extra-search-dir`` options to
	virtualenv like this::

	$ virtualenv --extra-search-dir=/path/to/distributions ENV

	The ``/path/to/distributions`` path should point to a directory that contains
	setuptools and/or pip wheels.

	virtualenv will look for wheels in the specified directories, but will use
	pip's standard algorithm for selecting the wheel to install, which looks for
	the latest compatible wheel.

	As well as the extra directories, the search order includes:

	#. The ``virtualenv_support`` directory relative to virtualenv.py
	#. The directory where virtualenv.py is located.
	#. The current directory.

	If no satisfactory local distributions are found, virtualenv will
	fail. Virtualenv will never download packages.