title: TypeError: 'dict_keys' object does not support indexing
body: <pre><code>def shuffle(self, x, random=None, int=int):
      """x, random=random.random -&gt; shuffle list x in place; return None.
  
      Optional arg random is a 0-argument function returning a random
      float in [0.0, 1.0); by default, the standard random.random.
      """
  
      randbelow = self._randbelow
      for i in reversed(range(1, len(x))):
          # pick an element in x[:i+1] with which to exchange x[i]
          j = randbelow(i+1) if random is None else int(random() * (i+1))
          x[i], x[j] = x[j], x[i]
  </code></pre>
  
  <p>When I run the <code>shuffle</code> function it raises the following error, why is that?</p>
  
  <pre><code>TypeError: 'dict_keys' object does not support indexing
  </code></pre>