title: Make a list of ints hashable in python
body: <p>I have a lists of integers that I would like to use as keys in python dictionaries.  I'm caching results from a function(s) that takes a list of ints as input.  My current solution:</p>
  
  <pre><code>list_of_ints = [1,20,3,4]
  key = str(sorted(list_of_ints))[1:-1].replace(' ','')
  </code></pre>
  
  <p>which generates the key '1,3,4,20'.  Seems like there should be a faster/prettier/more-pythonic way to do this.</p>