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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 get_unavailable_brokers(zk, partition_metadata):
 """Returns the set of unavailable brokers from the difference of replica set of given partition to the set of available replicas. """

    topic_data = zk.get_topics(partition_metadata.topic)
    topic = partition_metadata.topic
    partition = partition_metadata.partition
    expected_replicas = set(topic_data[topic]['partitions'][str(partition)]['replicas'])
    available_replicas = set(partition_metadata.replicas)
    return expected_replicas - available_replicas