title: Pandas set_Value with DatetimeIndex [Python]
body: <p>I'm trying to add the row-wise result from a function into my dataframe using 
  <code>df.set_Value</code>.</p>
  
  <p><code>df</code> in the format :</p>
  
  <pre><code>    Count   DTW
  DateTime        
  2015-01-16  10  0
  2015-01-17  28  0
  </code></pre>
  
  <p>Using <code>df.setValue</code></p>
  
  <pre><code>dw.set_Value(idx, 'col', dtw) # idx and dtw are int values
  
  TypeError: cannot insert DatetimeIndex with incompatible label
  </code></pre>
  
  <p>How do I solve this error or what alternative method with comparable efficiency is there?</p>