title: How to perform slicing of a data frame using datetimes?
body: <p>I have a <code>pandas.DataFrame</code> <code>df1</code>, indexed with a <code>pandas.DateRange</code> object.</p>
  
  <p>If I have a <code>d1</code> and <code>d2</code>, as datetimes, why does <code>df[d1:d2]</code>not work, and how can I obtain this slice?</p>