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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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()