def latest_metadata(self):
        """Returns segment metadata from the latest segment"""
        client = self.cluster.get_pydruid_client()
        results = client.time_boundary(datasource=self.datasource_name)
        if not results:
            return
        max_time = results[0]['result']['maxTime']
        max_time = parse(max_time)
        # Query segmentMetadata for 7 days back. However, due to a bug,
        # we need to set this interval to more than 1 day ago to exclude
        # realtime segments, which trigged a bug (fixed in druid 0.8.2).
        # https://groups.google.com/forum/#!topic/druid-user/gVCqqspHqOQ
        intervals = (timedelta(days=7) - max_time).isoformat() + '/'
        intervals += (max_time - timedelta(days=1)).isoformat()
        segment_metadata = client.segment_metadata(
            datasource=self.datasource_name,
            intervals=intervals)
        if segment_metadata:
            return segment_metadata[-1]['columns']
dataset/ETHPy150Open airbnb/caravel/caravel/models.py/DruidDatasource.latest_metadata/swapped operands of `-`