title: The difference between double brace `[[...]]` and single brace `[..]` indexing in Pandas
body: <p>I'm confused about the syntax regarding the following line of code: </p>
  
  <pre><code>x_values = dataframe[['Brains']]
  </code></pre>
  
  <p>The dataframe object consists of 2 columns (Brains and Bodies)</p>
  
  <pre><code>Brains Bodies
  42     34
  32     23
  </code></pre>
  
  <p>When I print x_values I get something like this:</p>
  
  <pre><code>Brains
  0  42
  1  32
  </code></pre>
  
  <p>I'm aware of the pandas documentation as far as attributes and methods of the dataframe object are concerned, but the double bracket syntax is confusing me.</p>