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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 ensure_sink(self):
 """Ensure the log sink and its pub sub topic exist."""

        topic_info = self.pubsub.ensure_topic()
        scope, sink_path, sink_info = self.get_sink(topic_info)
        client = self.session.client('logging', 'v2', '%s.sinks' % scope)
        try:
            sink = client.execute_command('get', {'sinkName': sink_path})
        except HttpError as e:
            if e.resp.status != 404:
                raise
            sink = client.execute_command('create', sink_info)
        else:
            delta = delta_resource(sink, sink_info['body'])
            if delta:
                sink_info['updateMask'] = ','.join(delta)
                sink_info['sinkName'] = sink_path
                sink_info.pop('parent')
                sink = client.execute_command('update', sink_info)
            else:
                return sink_path

        self.pubsub.ensure_iam(publisher=sink['writerIdentity'])
        return sink_path