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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 participant_policy(self, value):
 """ Changing participation policy fires a "ParticipationPolicyChanged" event """

        old_policy = self.participant_policy
        new_policy = value
        self._participant_policy = new_policy
        notify(ParticipationPolicyChangedEvent(self, old_policy, new_policy))