If you're a python programmer, you've most likely heard of [virtualenv][a]. If you haven't, then you need to check it out.
virtualenv is a tool to create isolated Python environments.
In a nutshell, you can create as many virtual environments as you want. Each of these virtual environments is a small directory structure, which contains a copy of your python interpreter(s), and provides a sandbox environment in which you can install only the necessary packages you need to run your project, as well as remove your programs' dependence on system packages and python versions.