title: Python How to find duplicate values in Dictionary
body: <p>Okay I was wondering how I can find duplicate values for a single key in a dictionary.</p>
  
  <p>so I have</p>
  
  <pre><code>import collections
  s = [('yellow', 1), ('blue', 2), ('yellow', 1), ('blue', 4), ('red', 1)]
  d = collections.defaultdict(list)
  for k, v in s:
      d[k].append(v)
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>defaultdict(&lt;class 'list'&gt;, {'blue': [2, 4], 'yellow': [1, 1], 'red': [1]})
  </code></pre>
  
  <p>As you can see "Yellow" has duplicate values.</p>
  
  <p>I was wondering, what is the best pythonic way of finding out if there are duplicate values within a key in the dictionary. And after finding them, removing them from the dictionary.</p>