A Virtual Environment is a tool to keep the dependencies required by different projects in separate places, by creating virtual Python environments for them. It solves the “Project X depends on version 1.x but, Project Y needs 4.x” dilemma, and keeps your global site-packages directory clean and manageable. For example, you can work on a project which requires Django 1.3 while also maintaining a project which requires Django 1.0. ¹⁾

The python virtual environment package is installed by default on most CS machines. To make sure you can do the following:

user@computer:~/projects$ which virtualenv
/usr/bin/virtualenv

user@hester:~/projects$ virtualenv --no-site-packages exampleproject
The --no-site-packages flag is deprecated; it is now the default behavior.
New python executable in exampleproject/bin/python
Installing
distribute................................................................................done.
Installing pip...............done.

user@computer:~/projects$ ls -l exampleproject/
total 4
drwxrwxr-x 2 user group 4096 Nov 25 10:16 bin
drwxrwxr-x 2 user group   30 Nov 25 10:16 include
drwxrwxr-x 3 user group   30 Nov 25 10:16 lib
drwxrwxr-x 2 user group   56 Nov 25 10:16 local

user@computer:~/projects$ cd exampleproject/

Now you need to activate your virtual environment. This will setup some path variables to make the evironments bin and lib directory to be the default.

user@computer:~/projects/exampleproject$ source bin/activate
(exampleproject)user@computer:~/projects/exampleproject$ 

To deactivate or stop working on your environment use the fuction that gets sourced when you activate your environment:

(exampleproject)user@computer:~/projects/exampleproject$ deactivate
user@computer:~/projects/exampleproject$ 

virtualenvwrappers goal is to make virtualenv easier to use… sort of like when iTunes automatically organizes your iTunes library.

This creates the exampleproject folder inside ~/Envs.

user@computer:~/$ mkvirtualenv venv

'virtualenvwrapper' provides tab-completion on environment names. It really helps when you have a lot of environments and have trouble remembering their names. 'workon' also deactivates whatever environment you are currently in, so you can quickly switch between environments.

user@computer:~/$ workon venv

Deactivating is still the same:

user@computer:~/$ deactivate

To delete:

user@computer:~/$ rmvirtualenv venv

lsvirtualenv
  List all of the environments.
cdvirtualenv
  Navigate into the directory of the currently activated virtual environment, 
  so you can browse its site-packages, for example.
cdsitepackages
  Like the above, but directly into site-packages directory.
lssitepackages
  Shows contents of site-packages directory.