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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 add_subscriber(self, connection_id, subscriptions, last_known_block_id):
 """Register the subscriber for the given event subscriptions. Raises: InvalidFilterError One of the filters in the subscriptions is invalid. """

        with self._subscribers_cv:
            self._subscribers[connection_id] = \
                EventSubscriber(
                    connection_id, subscriptions, last_known_block_id)

        LOGGER.debug(
            'Added Subscriber %s for %s', connection_id, subscriptions)