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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 set_model(self, model):
 """Set all levels\' model to the given one :param m: the model that the levels should use :type m: QtCore.QAbstractItemModel :returns: None :rtype: None :raises: None """

        # do the set model in reverse!
        # set model might trigger an update for the lower levels
        # but the lower ones have a different model, so it will fail anyways
        # this way the initial state after set_model is correct.
        self.model = model
        self._levels[0].set_model(model)