title: merging several python dictionaries
body: <p>I have to merge list of python dictionary. For eg:</p>
  
  <pre><code>dicts[0] = {'a':1, 'b':2, 'c':3}
  dicts[1] = {'a':1, 'd':2, 'c':'foo'}
  dicts[2] = {'e':57,'c':3}
  
  super_dict = {'a':[1], 'b':[2], 'c':[3,'foo'], 'd':[2], 'e':[57]}    
  </code></pre>
  
  <p>I wrote the following code:</p>
  
  <pre><code>super_dict = {}
  for d in dicts:
      for k, v in d.items():
          if super_dict.get(k) is None:
              super_dict[k] = []
          if v not in super_dict.get(k):
              super_dict[k].append(v)
  </code></pre>
  
  <p><em>Can it be presented more elegantly / optimized?</em></p>
  
  <p><strong>Note</strong>
  I found another <a href="https://stackoverflow.com/questions/2365921/merging-python-dictionaries">question</a> on SO but its about merging exactly 2 dictionaries.</p>