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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_broker(self, broker):
 """Add broker to current broker-list."""

        if broker not in self._brokers:
            self._brokers.add(broker)
        else:
            self.log.warning(
                'Broker {broker_id} already present in '
                'replication-group {rg_id}'.format(
                    broker_id=broker.id,
                    rg_id=self._id,
                )
            )