title: Attempt to access dataframe column displays "<bound method NDFrame.xxx..."
body: <p>I create DataFrame object in Jupyter notebook:</p>
  
  <pre><code>data = {'state':['Ohio','Ohio','Ohio','Nevada','Nevada'],
         'year':[2000, 2001, 2002, 2000, 2001],
         'pop':[1.5, 2.0, 3.6, 2.4, 2.9]}
  frame = DataFrame(data)
  </code></pre>
  
  <p>When I'm extracting column 'year', it's ok:</p>
  
  <pre><code>In [30]: frame.year
  Out[30]: 0    2000
           1    2001
           2    2002
           3    2000
           4    2001
           Name: year, dtype: int64
  </code></pre>
  
  <p>But when I'm extracting column 'pop' (frame.pop), result is:</p>
  
  <pre><code>Out[31]:
  &lt;bound method NDFrame.pop of    pop   state  year
  0  1.5    Ohio  2000
  1  2.0    Ohio  2001
  2  3.6    Ohio  2002
  3  2.4  Nevada  2000
  4  2.9  Nevada  2001&gt;
  </code></pre>
  
  <p>Why the result is not the same as for "frame.year"?</p>