title: unhashable type: 'dict' Type Error
body: <p>Suppose I have this dictionary:</p>
  
  <pre><code>items = {1: {'title': u'testing123', 'description': u'testing456'},
  2: {'description': u'testing123', 'description': u'testing456'},
  3: {'description': u'testing123', 'description': u'testing456'},
  4: {'description': u'testing123', 'description': u'testing456'},
  5: {'description': u'testing123', 'description': u'testing456'},
  6: {'description': u'somethingelse', 'description': u'somethingelse'}}
  </code></pre>
  
  <p>I want to filter out the duplicate values, so that in the end I'd get </p>
  
  <pre><code>{1: {'title': u'testing123', 'description': u'testing456'}, 6: {'title': u'something', 'description': u'somethingelse'}}
  </code></pre>
  
  <p>I wrote this code:</p>
  
  <pre><code>dic = {}
  
  for key, value in items.items():
      if not set(value.values()).issubset(set(dic.values())):
          dic[key] = value
  </code></pre>
  
  <p>however I get the error message <code>TypeError: unhashable type: 'dict'</code>. I am not sure why this happens and how to fix it. </p>
  
  <p>This is inspired by <a href="https://stackoverflow.com/questions/27435395/removing-duplicate-items-by-value-within-a-dict">another question</a> and my failed attempt to solve it. </p>