Aims:

Set up a python environment where I can run multiple self contained versions of python under virtualenv.

URLs used:

• http://docs.python-guide.org/en/latest/dev/virtualenvs/
• http://dabapps.com/blog/introduction-to-pip-and-virtualenv-python/
• http://virtualenvwrapper.readthedocs.org/en/latest/

TL;DR

• Do use pip
• Don't use easy-install (apart from to install pip)
• Do install virtualenv
• Don't use virtualenv to manage virtual environments
• Do install virtualenvwrapper
• Do use virtualenvwrapper to manage virtual environments

SetUpCode:

sudo pip install virtualenv   
sudo pip install virtualenvwrapper
sudo geany .bashrc
<addTheFollowingToBashrc>
    # set the workonhome and virtualenvwrapper_python
    export WORKON_HOME=$HOME/.virtualenvs
    export VIRTUALENVWRAPPER_PYTHON=/usr/bin/python3.4
    source /usr/bin/virtualenvwrapper.sh
</addTheFollowingToBashrc>

Useage:

mkvirtualenv <virtualenvironment name> #create a virtual environment using default settings
mkvirtualenv -p /usr/bin/python3.4 <virtualenvironment name> #create a virtual environment using python3.4
mkvirtualenv -p /usr/bin/python2.7 <virtualenvironment name> #create a virtual environment using python2.7
lsvirtualenv #List the virtual enviornments: 
workon <virtualenvironment name> #Use a specific virtual environment
rmvirtualenv <virtualenvironment name> #Remove a specific virtual environment
deactivate #stop using the current virtual environment

Why:

By forcing your code to work against self-contained python environments stored in unique 'virtual environments' you insulate yourself from changes in the underlying libraries which may break your code.

What does virtualenv do:

virtualenv solves this problem by creating a completely isolated virtual environment for each of your programs. An environment is simply a directory that contains a complete copy of everything needed to run a Python program, including a copy of the python binary itself, a copy of the entire Python standard library, a copy of the pip installer, and (crucially) a copy of the site-packages directory mentioned above. When you install a package from PyPI using the copy of pip that's created by the virtualenv tool, it will install the package into the site-packages directory inside the virtualenv directory. You can then use it in your program just as before.

What does virtualenvwrapper do:

• Organizes all of your virtual environments in one place.
• Wrappers for managing your virtual environments (create, delete, copy).
• Use a single command to switch between environments.
• Tab completion for commands that take a virtual environment as argument.
• User-configurable hooks for all operations (see Per-User Customization).
• Plugin system for more creating sharable extensions (see Extending Virtualenvwrapper).