docs: def add(self, classifier, threshold, begin=None, end=None):
      """Adds a new strong classifier with the given threshold to the cascade.
  
      **Parameters:**
  
      classifier : :py:class:`bob.learn.boosting.BoostedMachine`
        A strong classifier to add
  
      ``threshold`` : float
        The classification threshold for this cascade step
  
      ``begin``, ``end`` : int or ``None``
        If specified, only the weak machines with the indices ``range(begin,end)`` will be added.
      """
      boosted_machine = bob.learn.boosting.BoostedMachine()
      if begin is None: begin = 0
      if end is None: end = len(classifier.weak_machines)
      for i in range(begin, end):
        boosted_machine.add_weak_machine(classifier.weak_machines[i], classifier.weights[i])
      self.cascade.append(boosted_machine)
      self.thresholds.append(threshold)
      self._indices()