title: filter out symmetrical lines by python
body: <p>I have a graphviz file automatically generated, which sometimes produces double connections, e.g.</p>
  
  <pre><code>"test textanalysis" -&gt; "development" [color="white"];
  "development" -&gt; "test textanalysis" [color="white"];
  </code></pre>
  
  <p>I'd like to know </p>
  
  <p>1) if it is possible to show this as a single connection with double arrows at start&amp;end in Graphviz</p>
  
  <p>2) or in alternative if you know a Python way to filter out one of those lines (I dont mind losing that information): I cannot find a regex able to do it!</p>