title: Pandas: Get label for value in Series Object
body: <p>How is it possible to retrieve the labe of a particular value in a pandas Series object:</p>
  
  <p>For example:</p>
  
  <pre><code>labels = ['a', 'b', 'c', 'd', 'e']
  s = Series (arange(5) * 4 , labels)
  </code></pre>
  
  <p>Which produces the Series:</p>
  
  <pre><code>a     0
  b     4
  c     8
  d    12
  e    16
  dtype: int64
  </code></pre>
  
  <p>How is it possible to get the label of value '12'? Thanks</p>