title: Pandas - Selecting rows in a DataFrame using String equality
body: <p>I am trying to get all rows from the DataFrame <code>contributors</code> where occupation is retired, like so:</p>
  
  <pre><code>mask = (contributors.contbr_occupation.str == 'RETIRED')
  print(contributors[mask])
  </code></pre>
  
  <p>However, I get the following stack trace:</p>
  
  <pre><code>Traceback (most recent call last):
    File "C:\Users\Me\Anaconda3\envs\pandas\lib\site-packages\pandas\indexes\base.py", line 2134, in get_loc
      return self._engine.get_loc(key)
    File "pandas\index.pyx", line 132, in pandas.index.IndexEngine.get_loc (pandas\index.c:4433)
    File "pandas\index.pyx", line 154, in pandas.index.IndexEngine.get_loc (pandas\index.c:4279)
    File "pandas\src\hashtable_class_helper.pxi", line 732, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:13742)
    File "pandas\src\hashtable_class_helper.pxi", line 740, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:13696)
  KeyError: False
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "census_attack.py", line 27, in &lt;module&gt;
      print(contributors[mask])
    File "C:\Users\Me\Anaconda3\envs\pandas\lib\site-packages\pandas\core\frame.py", line 2059, in __getitem__
      return self._getitem_column(key)
    File "C:\Users\Me\Anaconda3\envs\pandas\lib\site-packages\pandas\core\frame.py", line 2066, in _getitem_column
      return self._get_item_cache(key)
    File "C:\Users\Me\Anaconda3\envs\pandas\lib\site-packages\pandas\core\generic.py", line 1386, in _get_item_cache
      values = self._data.get(item)
    File "C:\Users\Me\Anaconda3\envs\pandas\lib\site-packages\pandas\core\internals.py", line 3543, in get
      loc = self.items.get_loc(item)
    File "C:\Users\Me\Anaconda3\envs\pandas\lib\site-packages\pandas\indexes\base.py", line 2136, in get_loc
      return self._engine.get_loc(self._maybe_cast_indexer(key))
    File "pandas\index.pyx", line 132, in pandas.index.IndexEngine.get_loc (pandas\index.c:4433)
    File "pandas\index.pyx", line 154, in pandas.index.IndexEngine.get_loc (pandas\index.c:4279)
    File "pandas\src\hashtable_class_helper.pxi", line 732, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:13742)
    File "pandas\src\hashtable_class_helper.pxi", line 740, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:13696)
  KeyError: False
  </code></pre>
  
  <p>How can I do this?</p>