title: pandas category column - why does .apply allow access to interval properties?
body: <p>In <a href="https://stackoverflow.com/a/55689156/10595996">this answer</a>, we can see that pd.cut() results in a column of type category and that .apply() allows access to the properties of a given interval value.</p>
  <p>For example, this works:</p>
  <pre><code>df['b'] = df['a'].apply(lambda x: x.left)
  </code></pre>
  <p>But this does not work:</p>
  <pre><code>df['b'] = df['a'].left
  </code></pre>
  <p>I don't understand why this is. Couldn't find a good explanation. If someone can explain, that would be great.</p>