title: Python dictionary : TypeError: unhashable type: 'list'
body: <p>I'm having troubles in populating a python dictionary starting from another dictionary.</p>
  
  <p>Let's assume that the "source" dictionary has string as keys and has a list of custom objects per value.</p>
  
  <p>I'm creating my target dictionary exactly as I have been creating my "source" dictionary how is it possible this is not working ?</p>
  
  <p>I get </p>
  
  <pre><code>TypeError: unhashable type: 'list'
  </code></pre>
  
  <p>Code :</p>
  
  <pre><code>aTargetDictionary = {}
  for aKey in aSourceDictionary:
      aTargetDictionary[aKey] = []
      aTargetDictionary[aKey].extend(aSourceDictionary[aKey])
  </code></pre>
  
  <p>The error is on this line : <code>aTargetDictionary[aKey] = []</code></p>