title: What's the proper way to slice `self` within a method of a List subclass?
body: <p>I intend to create a method to slice a <code>list</code>, however I don't have the correct syntax here, and I haven't been able to come up with the correct search query to find out how to do this:</p>
  
  <pre><code>class BarList(list):
      """Items in the list are always in ascending order of .date"""
      def trim(self, start:dt.datetime=None, end:dt.datetime=None):
          """Removes all bars before `start` and after `end`"""
          if start:
              for i, bar in enumerate(self):
                  if bar.date &gt;= start:
                      self = self[i:]
                      break
  </code></pre>
  
  <p>What's the proper way to do what I'm trying to express in the above pseudocode?</p>