code: def add(self, revision, operators):
          
          ir = IndexedRevision(
              revision=revision, operators=[operator.name for operator in operators]
          )
          self._revisions[revision.key] = ir
          return ir
docs: Add a revision to the index.
  
          :param revision: The revision.
          :type  revision: :class:`Revision` or :class:`LazyRevision`