title: how to get specific nodes in xml file with python
body: <p>im searching for a way to get a specific tags .. from a very big xml document 
  with python dom built in module
  <br>
  for example :<br></p>
  
  <pre><code>&lt;AssetType longname="characters" shortname="chr" shortnames="chrs"&gt;
    &lt;type&gt;
      pub
    &lt;/type&gt;
    &lt;type&gt;
      geo
    &lt;/type&gt;
    &lt;type&gt;
      rig
    &lt;/type&gt;
  &lt;/AssetType&gt;
  
  &lt;AssetType longname="camera" shortname="cam" shortnames="cams"&gt;
    &lt;type&gt;
      cam1
    &lt;/type&gt;
    &lt;type&gt;
      cam2
    &lt;/type&gt;
    &lt;type&gt;
      cam4
    &lt;/type&gt;
  &lt;/AssetType&gt;
  </code></pre>
  
  <p>i want to retrieve the value of children of AssetType node who got attribute (longname= "characters" )
  to have the result of <code>'pub','geo','rig'</code><br>
  please put in mind that i have more than 1000 &lt; AssetType> nodes 
  <br>
  thanx in advance</p>