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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 exec_event_handler(self, event, transactional=False):
 """Execute the Async set to be run on event."""

        # QUESTION: Should we raise an exception if `event` is not in some
        # known event-type list?

        callbacks = self._options.get('callbacks', {})

        handler = callbacks.get(event)

        if not handler:
            raise Exception('Handler not defined!!!')

        handler.start(transactional=transactional)