title: How to get row, column indices of all non-NaN items in Pandas dataframe
body: <p>How do I iterate over a dataframe like the following and return the non-NaN value locations as a tuple. i.e.</p>
  
  <pre><code>df:
  
       0    1    2
  0    NaN NaN   1
  1    1   NaN  NaN
  2    NaN  2   NaN
  </code></pre>
  
  <p>I would get an output of [(0, 1), (2, 0), (1, 2)].  Would the best way be to do a nested-for loop? Or is there an easier way I'm unaware of through Pandas.</p>