title: Python: finding keys with unique values in a dictionary?
body: <p>I receive a dictionary as input, and want to return a list of keys for which the dictionary values are unique in the scope of that dictionary.</p>
  
  <p>I will clarify with an example. Say my input is dictionary a, constructed as follows:</p>
  
  <pre><code>a = dict()
  a['cat'] =      1
  a['fish'] =     1
  a['dog'] =      2  # &lt;-- unique
  a['bat'] =      3
  a['aardvark'] = 3
  a['snake'] =    4  # &lt;-- unique
  a['wallaby'] =  5
  a['badger'] =   5  
  </code></pre>
  
  <p>The result I expect is <code>['dog', 'snake']</code>.</p>
  
  <p>There are obvious brute force ways to achieve this, however I wondered if there's a neat Pythonian way to get the job done.</p>