code: def tiles_of_interest(self):
          
  
          # also return back whether the response was cached
          # useful for metrics
          is_cached = False
  
          get_options = dict(
              Bucket=self.bucket,
              Key=self.key,
          )
          if self.etag:
              get_options['IfNoneMatch'] = self.etag
          try:
              resp = self.s3_client.get_object(**get_options)
          except Exception as e:
              # boto3 client treats 304 responses as exceptions
              if isinstance(e, ClientError):
                  resp = getattr(e, 'response', None)
                  assert resp
              else:
                  raise e
          status_code = resp['ResponseMetadata']['HTTPStatusCode']
          if status_code == 304:
              assert self.prev_toi
              toi = self.prev_toi
              is_cached = True
          elif status_code == 200:
              body = resp['Body']
              try:
                  gzip_payload = body.read()
              finally:
                  try:
                      body.close()
                  except Exception:
                      pass
              gzip_file_obj = StringIO(gzip_payload)
              toi = load_set_from_gzipped_fp(gzip_file_obj)
              self.prev_toi = toi
              self.etag = resp['ETag']
          else:
              assert 0, 'Unknown status code from toi get: %s' % status_code
  
          return toi, is_cached
docs: conditionally get the toi from s3