title: Pandas 'bool object is not callable'
body: <p>I have a dataframe with several columns, and I'm trying to group it in respect to a column and sort it according to another column.
  If I apply groupby() like this:</p>
  
  <pre><code>data.groupby(columnA)
  </code></pre>
  
  <p>it doesn't spit out any errors, yet if I try to sort it like this:</p>
  
  <pre><code>data.groupby(columnA).sort(coulmnB)
  </code></pre>
  
  <p>it gives me</p>
  
  <pre><code>TypeError: 'bool' object is not callable
  </code></pre>
  
  <p>I don't have any bool objects in any of the columns, and totally clueless about why this error is occuring.
  How would I solve this problem? If I'm totally doing it wrong, what's another way to group, and sort a DataFrame according to two different columns?
  Thanks in advance.</p>