code: def _save_stats(self, epoch_data: EpochData) -> None:
          
  
          for stream_name in epoch_data.keys():
              for variable, aggregations in self._variable_aggregations.items():
                  # variables are already checked in the AccumulatingHook; hence, we do not check them here
                  epoch_data[stream_name][variable] = OrderedDict(
                      {aggr: ComputeStats._compute_aggregation(aggr, self._accumulator[stream_name][variable])
                       for aggr in aggregations})
docs: Extend ``epoch_data`` by stream:variable:aggreagation data.
  
          :param epoch_data: data source from which the statistics are computed