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# VirtualEnv

`VirtualEnv` is a tool that you can use to keep your Python path clean and tidy. It allows you to install new packages and all of their dependencies into a clean working environment, thus eliminating the possibility that installing turbogears or some other new package will break your existing Python environment.

The other great advantage of VirtualEnv is that it allows you to run multiple versions of the same package in parallel which is great for running both the production version and the development version of an application on the same machine.

People with a sys-admin background could consider VirtualEnv as a variation of an OS jail (chroot) which is also good for security as your installation is totally isolated. This makes VirtualEnv great for deploying production sites.

We strongly advise you to install all your TurboGears apps inside a VirtualEnv. If you ask for support without a VirtualEnv to isolate your packages we will usually ask you to go get VirtualEnv before proceeding further.

## Installing `VirtualEnv`

On Windows:

    easy_install virtualenv

On Unix:

    $ sudo easy_install virtualenv

On Unix (non-root):

    $ easy_install --install-dir=$HOME/lib/python2.5/ --script-dir=$HOME/bin/ virtualenv

will output something like:

    Searching for virtualenv
    Reading http://pypi.python.org/simple/virtualenv/
    Best match: virtualenv 1.3.2
    Downloading http://pypi.python.org/packages/2.5/v/virtualenv/virtualenv-1.3.2-py2.5.egg#md5=1db8cdd823739c79330a138327239551
    Processing virtualenv-1.3.2-py2.5.egg
    .....
    Processing dependencies for virtualenv
    Finished processing dependencies for virtualenv

## Creating a VirtualEnv

Basic VirtualEnv usage is as follows:

    $virtualenv example

Normally you will want to create a VirtualEnv which does not use system packages as system packages can conflict with the TurboGears-installed packages.

    $virtualenv --no-site-packages example

You may also want to create a VirtualEnv that uses a version of Python other than the default Python on your platform.

    $virtualenv -p python2.5 example

## Activate Your VirtualEnv

First go inside the VirtualEnv:

    $ cd tg2env

On Windows you activate a VirtualEnv with the command:

    Scripts\activate.bat

On UNIX you activate a VirtualEnv with the command:

    $ source bin/activate

If you are on Unix your prompt should change to indicate that you’re in a VirtualEnv. It will look something like this:

    (tg2env)username@host:~/tg2env$

The net result of activating your VirtualEnv is that your PATH variable now points to the tools in tg2evn/bin and your python will look for libraries in tg2evn/lib.

Therefore you need to reactivate your VirtualEnv every time you want to work on your `tg2env` environment.

## Deactivating (Escaping) VirtualEnv

On Win32, you deactivate the VirtualEnv via:

    Scripts\deactivate.bat

and on Linux:

    deactivate

## Further Information

The VirtualEnv page on PyPI provides links to usage, documentation and the like.