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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 _as_published_topic(self):
 """This stream as a PublishedTopic if it is published otherwise None """


        oop = self.get_operator_output_port()
        if not hasattr(oop, 'export'):
            return

        export = oop.export
        if export['type'] != 'properties':
            return

        seen_export_type = False
        topic = None

        for p in export['properties']:
            if p['type'] != 'rstring':
                continue
            if p['name'] == '__spl_exportType':
                if p['values'] == ['"topic"']:
                    seen_export_type = True
                else:
                    return
            if p['name'] == '__spl_topic':
                topic = p['values'][0]

        if seen_export_type and topic is not None:
            schema = None
            if hasattr(oop, 'tupleAttributes'):
                ta_url = oop.tupleAttributes
                ta_resp = self.rest_client.make_request(ta_url)
                schema = streamsx.topology.schema.StreamSchema(ta_resp['splType'])
            return PublishedTopic(topic[1:-1], schema)
        return