docs: def hydrate_spawned_files(self, exported_files_mapper, filename, data_id):
          """Pop the given file's map from the exported files mapping.
  
          :param exported_files_mapper: The dict of file mappings this
              process produced.
          :param filename: The filename to format and remove from the
              mapping.
          :param data_id: The id of the :meth:`~resolwe.flow.models.Data`
              object owning the mapping.
          :return: The formatted mapping between the filename and
              temporary file path.
          :rtype: dict
          """
          # JSON only has string dictionary keys, so the Data object id
          # needs to be stringified first.
          data_id = str(data_id)
  
          if filename not in exported_files_mapper[data_id]:
              raise KeyError("Use 're-export' to prepare the file for spawned process: {}".format(filename))
  
          export_fn = exported_files_mapper[data_id].pop(filename)
  
          if exported_files_mapper[data_id] == {}:
              exported_files_mapper.pop(data_id)
  
          return {'file_temp': export_fn, 'file': filename}