title: How to cycle the NaNs in pandas dataframe rows?
body: <p>I have a dataframe like this:</p>
  
  <pre class="lang-py prettyprint-override"><code>df = pd.DataFrame({0: list('wxyz'), 1: [1,2,None,None], 2: [10,20,30,None]}).T
  print(df)
  
      0   1    2    3
  0   w   x    y    z
  1   1   2  NaN  NaN
  2  10  20   30  NaN
  </code></pre>
  
  <p>How to put all the NAs in the left instead of right?</p>
  
  <p>Required:</p>
  
  <pre><code>    0   1    2    3
  0   w   x    y    z
  1  NaN  NaN  1    2
  2  NaN  10  20   30
  </code></pre>