title: Finding label location in a DataFrame Index
body: <p>I have a pandas dataframe:</p>
  
  <pre><code>import pandas as pnd
  d = pnd.Timestamp('2013-01-01 16:00')
  dates = pnd.bdate_range(start=d, end = d+pnd.DateOffset(days=10), normalize = False)
  
  df = pnd.DataFrame(index=dates, columns=['a'])
  df['a'] = 6
  
  print(df)
                       a
  2013-01-01 16:00:00  6
  2013-01-02 16:00:00  6
  2013-01-03 16:00:00  6
  2013-01-04 16:00:00  6
  2013-01-07 16:00:00  6
  2013-01-08 16:00:00  6
  2013-01-09 16:00:00  6
  2013-01-10 16:00:00  6
  2013-01-11 16:00:00  6
  </code></pre>
  
  <p>I am interested in find the label location of one of the labels, say,</p>
  
  <pre><code>ds = pnd.Timestamp('2013-01-02 16:00')
  </code></pre>
  
  <p>Looking at the index values, I know that is integer location of this label 1. How can get pandas to tell what the integer value of this label is?</p>