title: Python alternative to using List as Dictionary Key?
body: <p>I currently have a dictionary that maps normalized mutual information scores to aligned sites in a multiple sequence alignment, which are stored in a list. However, I've realized that two list may happen to have the same score. Thus only one list will be stored in the dictionary since the score is the key. Clusters should be unique though, so I'm not sure what to do since a my list doesn't have a hash function. </p>
  
  <p>This is what my data looks like. Ideally I would simply like to reverse the keys and values. </p>
  
  <pre><code>{
  0.475: [10, 11]
  0.434: [12, 14]
  0.404: [16, 18]
  0.341: [21, 22]
  }
  
  </code></pre>