code: def _get_file_handlers(self, dsid):
          
          ds_info = self.ids[dsid]
  
          filetype = self._preferred_filetype(ds_info['file_type'])
          if filetype is None:
              logger.warning("Required file type '%s' not found or loaded for "
                             "'%s'", ds_info['file_type'], dsid.name)
          else:
              return self.file_handlers[filetype]
docs: Get the file handler to load this dataset.