title: Python dict.get('key') versus dict['key']
body: <p>Why does this throw a KeyError:</p>
  
  <pre><code>d = dict()
  d['xyz']
  </code></pre>
  
  <p>But this does not?</p>
  
  <pre><code>d = dict()
  d.get('xyz')
  </code></pre>
  
  <p>I'm also curious if descriptors play a role here.</p>