title: Is there a 'multimap' implementation in Python?
body: <p>I am new to Python, and I am familiar with implementations of <a href="http://en.wikipedia.org/wiki/Multimap" rel="noreferrer">Multimaps</a> in <a href="http://www.sgi.com/tech/stl/Multimap.html" rel="noreferrer">other</a> <a href="http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Multimap.html" rel="noreferrer">languages</a>. Does Python have such a data structure built-in, or available in a commonly-used library?</p>
  
  <p>To illustrate what I mean by "multimap":</p>
  
  <pre><code>a = multidict()
  a[1] = 'a'
  a[1] = 'b'
  a[2] = 'c'
  
  print(a[1])  # prints: ['a', 'b']
  print(a[2])  # prints: ['c']
  </code></pre>