title: how to do a left,right and mid of a string in a pandas dataframe
body: <p>in a pandas dataframe how can I apply a sort of excel left('state',2) to only take the first two letters. Ideally I want to learn how to use left,right and mid in a dataframe too. So need an equivalent and not a "trick" for this specific example.</p>
  
  <pre><code>data = {'state': ['Auckland', 'Otago', 'Wellington', 'Dunedin', 'Hamilton'],
  'year': [2000, 2001, 2002, 2001, 2002],
  'pop': [1.5, 1.7, 3.6, 2.4, 2.9]}
  df = pd.DataFrame(data)
  
  print df
  
       pop       state  year
   0  1.5    Auckland  2000
   1  1.7       Otago  2001
   2  3.6  Wellington  2002
   3  2.4     Dunedin  2001
   4  2.9    Hamilton  2002
  </code></pre>
  
  <p>I want to get this:</p>
  
  <pre><code>    pop       state     year  StateInitial
   0  1.5       Auckland    2000     Au
   1  1.7       Otago       2001     Ot
   2  3.6       Wellington  2002     We
   3  2.4       Dunedin     2001     Du
   4  2.9       Hamilton    2002     Ha
  </code></pre>