title: Is there a function to add non null columns in python?
body: <pre><code>pd.DataFrame({'col1': [1, np.nan, np.nan, 4, 7],
  'col2': [4, 5, np.nan, 9, 5]})
  </code></pre>
  <p>I want sum of null values (col1, col2) to be null How it can be achieved?</p>
  <pre><code>d['SUM' ]=d[[ ' col1' , 'col2' ]]. sum (axis=1)
  d
  </code></pre>
  <p>With the sum function I got sum of null values as
  'O'</p>
  <pre><code>COl1 col2 SUM
  0 1.0 4.0 5.0
  1 NaN 5.0 5.0
  NaN NaN 0.0
  3 4.0 9.0 13.0
  4 7.0 5.0 12.0
  </code></pre>