title: Need a list of all units available in quantities python package
body: <p>I'm trying to get a list of all the units that are predefined in the python quantities package. Something like this:</p>
  
  <pre><code>from quantities import units as u
  
  myList = u.length.list(everything defined with UnitLength)
  </code></pre>
  
  <p>and the result would be:</p>
  
  <pre><code>myList = ['m','meter','metre,'mi','au',...]
  </code></pre>
  
  <p>I want to do that for all the unit types that they define in the package.  Any idea how to do that without parsing the actual source code?</p>