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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 supervisor(self):
 """Return an authenticated connection for use, open new if required. Returns: SupervisorWebService: New or existing session with the Five9 Statistics API. """

        supervisor = self._cached_client('supervisor')
        if not self._api_supervisor_session:
            self._api_supervisor_session = self.__create_supervisor_session(
                supervisor,
            )
        return supervisor