title: Adding elements to a dictionary of sets
body: <p>I have a dictionary <code>d</code> of sets. When adding an element under some key <code>key</code> I consider the two cases <code>key in d</code> and <code>not key in d</code>:</p>
  
  <pre><code>from random import randint
  
  for i in range(1000):
      key = randint(0, 100)
  
      if key in d:
          d[key] |= set([randint(0, 10)])
      else:
          d[key] = set([randint(0, 10])
  </code></pre>
  
  <p>Is there a cleaner way to do this? Can I unify the two cases?</p>