def get_topic_relevant_count(qrels, topic_num):
    """
    :param qrels: ifind.seeker.trec_qrel_handler.TrecQrelHandler
    Returns the number of documents considered relevant for topic topic_num.
    """
    count = 0

    for document in qrels.get_doc_list(topic_num):
        if qrels.get_value(topic_num, document) > 0:
            count = count + 1

    return count