docs: def get_compositions_by_repositories(self, repository_ids):
          """Gets the list of ``Compositions`` corresponding to a list of ``Repository`` objects.
  
          arg:    repository_ids (osid.id.IdList): list of repository
                  ``Ids``
          return: (osid.repository.CompositionList) - list of Compositions
          raise:  NullArgument - ``repository_ids`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method must be implemented.*
  
          """
          # Implemented from template for
          # osid.resource.ResourceBinSession.get_resources_by_bins
          composition_list = []
          for repository_id in repository_ids:
              composition_list += list(
                  self.get_compositions_by_repository(repository_id))
          return objects.CompositionList(composition_list)