title: Read a JSON and convert the keys to int
body: <p>It is well known that <code>json</code> converts integer keys of a dict to string:</p>
  
  <pre><code>import json
  print json.dumps({1: [2.5, 2.5, 2.5], 2: [3, 3, 3, 3]})
  # {"1": [2.5, 2.5, 2.5], "2": [3, 3, 3, 3]}
  </code></pre>
  
  <p>What's the cleanest way to restore integer keys when loading it back?</p>
  
  <pre><code>d = json.loads('{"1": [2.5, 2.5, 2.5], "2": [3, 3, 3, 3]}')
  print d
  # {u'1': [2.5, 2.5, 2.5], u'2': [3, 3, 3, 3]}
  </code></pre>
  
  <p>I was thinking about:</p>
  
  <pre><code>d = {int(k): d[k] for k in d}
  </code></pre>
  
  <p>but is there a cleaner way to deal with dictionaries with integer keys with JSON / Python, not requiring keys conversion a posteriori?</p>