code: def _elect_source_broker(self, victim_partition, broker_subset=None):
          
          broker_subset = broker_subset or self._brokers
          over_loaded_brokers = sorted(
              [
                  broker
                  for broker in broker_subset
                  if victim_partition in broker.partitions and not broker.inactive
              ],
              key=lambda b: len(b.partitions),
              reverse=True,
          )
          if not over_loaded_brokers:
              return None
  
          broker_topic_partition_cnt = [
              (broker, broker.count_partitions(victim_partition.topic))
              for broker in over_loaded_brokers
          ]
          max_count_pair = max(
              broker_topic_partition_cnt,
              key=lambda ele: ele[1],
          )
          return max_count_pair[0]
docs: Select first over loaded broker having victim_partition.
  
          Note: The broker with maximum siblings of victim-partitions (same topic)
          is selected to reduce topic-partition imbalance.