title: etree get attribute as a value instead of a string
body: <p>For a given Element, I want to check whether the <code>xsi:nil</code> attribute is set to true.</p>
  
  <p>My current code is</p>
  
  <pre><code>xsinil = dataFact.get('{http://www.w3.org/2001/XMLSchema-instance}nil', False)
  </code></pre>
  
  <p>But instead of being <code>True</code> xsinil is of type string...</p>
  
  <p>What's the best solution? I don't think this is very elegant:</p>
  
  <pre><code>xsinil=dataFact.get('{http://www.w3.org/2001/XMLSchema-instance}nil', False)
  if xsinil == 'true' or xsinil == '1' :
      xsinil = True
  </code></pre>