title: if key, value pair exist in a dictionary skip python
body: <p>I have two variables that I want to add to a dictionary using <code>collections.defaultdict(list)</code>
  Here are the two variables:</p>
  
  <pre><code>score = [0, 5, 7, 7, 8, 7]
  match = ['turtle', 'cat', 'horse', 'horse', 'dog', 'bear']
  </code></pre>
  
  <p>What I would like to do is to remove the key/value pairs that are already in the dictionary. Right now I am creating my dictionary using this method:</p>
  
  <pre><code>  scoring = collections.defaultdict(list)
    scoring[score].append(match)
  </code></pre>
  
  <p>However, this method gives me a dictionary like so:</p>
  
  <pre><code>dictionary = {0: ['turtle'], 5: ['cat'], 7: ['horse', 'horse', 'bear'], 8: ['dog']}
  </code></pre>
  
  <p>However, I only want horse to appear in the dictionary once. Is there anyway to prevent the additional of an identical key/value pair in a dictionary this way?</p>