code: def collect(self):  # pragma: NO COVER
          
          for v_name, view_data in self.view_name_to_data_map.items():
              if v_name not in self.registered_views:
                  continue
              desc = self.registered_views[v_name]
              for tag_values in view_data.tag_value_aggregation_data_map:
                  agg_data = view_data.tag_value_aggregation_data_map[tag_values]
                  metric = self.to_metric(desc, tag_values, agg_data)
                  yield metric
docs: Collect fetches the statistics from OpenCensus
          and delivers them as Prometheus Metrics.
          Collect is invoked every time a prometheus.Gatherer is run
          for example when the HTTP endpoint is invoked by Prometheus.