title: First non-null value per row from a list of Pandas columns
body: <p>If I've got a DataFrame in pandas which looks something like:</p>
  
  <pre><code>    A   B   C
  0   1 NaN   2
  1 NaN   3 NaN
  2 NaN   4   5
  3 NaN NaN NaN
  </code></pre>
  
  <p>How can I get the first non-null value from each row? E.g. for the above, I'd like to get: <code>[1, 3, 4, None]</code> (or equivalent Series).</p>