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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 _on_event(self, event):
 """ Returns the referential action for a given database operation on the referenced table the foreign key constraint is associated with. :param event: Name of the database operation/event to return the referential action for. :type event: str :rtype: str or None """

        if self.has_option(event):
            on_event = self.get_option(event).upper()

            if on_event not in ["NO ACTION", "RESTRICT"]:
                return on_event

        return False