title: How to get the indices list of all NaN value in numpy array?
body: <p>Say now I have a numpy array which is defined as,</p>
  
  <pre><code>[[1,2,3,4],
  [2,3,NaN,5],
  [NaN,5,2,3]]
  </code></pre>
  
  <p>Now I want to have a list that contains all the indices of the missing values, which is <code>[(1,2),(2,0)]</code> at this case.</p>
  
  <p>Is there any way I can do that?</p>