Implement as required by parent to lookup comments in file system.

def lookup_comments(self, reverse=False):
        "Implement as required by parent to lookup comments in file system."

        comments = []
        if self.thread_id is None:
            self.thread_id = self.lookup_thread_id()
        path = self.thread_id
        with open(self.thread_id, 'r', newline='') as fdesc:
            reader = csv.reader(fdesc)
            header = reader.__next__()
            assert header == self.header
            for num, line in enumerate(reader):
                if not line:
                    continue
                assert len(line) == len(header), (
                    'Line %i in path %s misformatted' % (num+1, path))
                line_kw = dict(zip(header, line))
                comments.append(SingleComment(**line_kw))
        if reverse:
            comments = list(reversed(comments))

        return CommentSection(comments)