title: Python dictionaries, key existence with fallback
body: <p>Is there any difference, gotcha or disadvantage between these approaches?</p>
  
  <pre><code>foo = dict(key=u"")
  bar = foo.get('key', 'foobar')
  </code></pre>
  
  <p>vs</p>
  
  <pre><code>foo = dict(key=u"")
  bar = bool(foo['key']) or 'foobar'
  </code></pre>