title: Removing duplicates from list of lists by using list comprehension
body: <p>I was curious if you could remove duplicates from list of lists and return uniques as a list. I was trying this:</p>
  
  <pre><code>def do_list( lists ):
      res = [ [ one for one in temp if one not in res ] for temp in lists ]
      return res
  </code></pre>
  
  <p>So for example, if:</p>
  
  <pre><code>lists = [ [ "a","b","c" ],[ "d","a" ],[ "c","a","f" ] ]
  </code></pre>
  
  <p>the result should be:</p>
  
  <pre><code>[ "a","b,"c","d","f" ]    
  </code></pre>
  
  <p>But it gives me error that I refference variable res before assigment.</p>