title: Python Dictionary return requested key if value does not exist
body: <p>I am looking for an easy way to be able to get a value from a dictionary, and if its not there, return the key that the user passed in.</p>
  
  <p>E.g.:</p>
  
  <pre><code>&gt;&gt;&gt; lookup = defaultdict(magic)
  &gt;&gt;&gt; print lookup['DNE']
  'DNE'
  &gt;&gt;&gt; print lookup.get('DNE')
  'DNE'
  &gt;&gt;&gt; print lookup['exists']
  'some other value'
  &gt;&gt;&gt; print lookup.get('exists')
  'some other value'
  </code></pre>
  
  <p>These will always be strings, but basically I am creating a language map and need an easy way to get a value, if it exists return it else return the key.</p>
  
  <p>Is there any easy way to do this?  Or should I just extend dict and do it manually.</p>