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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 fetch_offsets(zk, consumer_group, topics):
 """Fetch offsets for given topics of given consumer group. :param zk: Zookeeper client :param consumer_group: Consumer group id for given offsets :type consumer_group: int :rtype: dict(topic, dict(partition, offset)) """

    source_offsets = defaultdict(dict)
    for topic, partitions in six.iteritems(topics):
        for partition in partitions:
            offset, _ = zk.get(
                "/consumers/{groupid}/offsets/{topic}/{partition}".format(
                    groupid=consumer_group,
                    topic=topic,
                    partition=partition,
                )
            )
            source_offsets[topic][partition] = offset
    return source_offsets