@abc.abstractmethod<EOL><INDENT>def add_exception_event(self, time_period_id, event_id):<DEDENT>
pass<EOL>
Adds an exception event to a time period.

        Time period exception events govern exceptions to recurring
        events mapped to a time period.

        :param time_period_id: the ``Id`` of a ``TimePeriod``
        :type time_period_id: ``osid.id.Id``
        :param event_id: an exception event ``Id``
        :type event_id: ``osid.id.Id``
        :raise: ``AlreadyExists`` -- event is already part of the time period
        :raise: ``NotFound`` -- ``time_period_id`` or ``event_id`` is not found
        :raise: ``NullArgument`` -- ``time_period_id`` or ``event_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*