title: NumPy array is not JSON serializable
body: <p>After creating a NumPy array, and saving it as a Django context variable, I receive the following error when loading the webpage:</p>
  
  <pre><code>array([   0,  239,  479,  717,  952, 1192, 1432, 1667], dtype=int64) is not JSON serializable
  </code></pre>
  
  <p>What does this mean?</p>