title: Select python version to execute from prompt
body: <p>I have several python versions installed (and working properly on my machines). Isn't there a way to execute a specific version of python from the command line.</p>
  
  <p>Say I want to use python 3.1. I am after something a <strong><em>SIMPLE COMMAND</em></strong> such as <code>python3.1</code> or <code>python31</code> that would be used as follows :<code>python3.1 setup.py install</code>, for instance.</p>
  
  <p>[<code>pip</code> has <code>pip3.1</code> to install a library with the version 3.1 of python, specifically]</p>