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 Options):

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

   * "ENV/bin" is created, where executables live - noticeably a new
     **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 "ENV/bin/pip".

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


activate script
---------------

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

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

   $ source /path/to/ENV/bin/activate

For some shells (e.g. the original Bourne Shell) you may need to use
the **.** command, when **source** does not exist. There are also
separate activate files for some other shells, like csh and fish.
"bin/activate" should work for bash/zsh/dash.

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") then "sys.path" will
automatically be set to use the Python libraries associated with the
virtualenv. But, unlike the activation scripts, the environment
variables "PATH" and "VIRTUAL_ENV" will *not* be modified. This means
that if your Python script uses e.g. "subprocess" to run another
Python script (e.g. via a "#!/usr/bin/env python" shebang line) the
second script *may not be executed with the same Python binary as the
first* nor have the same libraries available to it. To avoid this
happening your first script will need to modify the environment
variables in the same manner as the activation scripts, before the
second script is executed.

The "activate" script will also modify your shell prompt to indicate
which environment is currently active. To disable this behaviour, see
"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 prompted 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.


Removing an Environment
-----------------------

Removing a virtual environment is simply done by deactivating it and
deleting the environment folder with all its contents:

   (ENV)$ deactivate
   $ rm -r /path/to/ENV


The "--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 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 or mod_wsgi
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 "--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 "--
system-site-packages" option will be implied.


The "--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:

1. The "virtualenv_support" directory relative to virtualenv.py

2. The directory where virtualenv.py is located.

3. The current directory.
