code: def get_dataset(self, ds_name, mode='r'):
          
          if ds_name in self._datasets:
              return self._datasets[ds_name]
          else:
              return self.create_empty_dataset(ds_name)
docs: Returns a h5py dataset given its registered name.
  
          :param ds_name: string
          Name of the dataset to be returned.
  
          :return: