code: def id_getter(self, relation_name, strict=False):
      
      def get_id(old_id):
        """Get the new ID for the enclosed relation, given an old ID."""
        return self.get_new_id(relation_name, old_id, strict)
      return get_id
docs: Returns a function that accepts an old_id and returns the new ID for the enclosed relation
      name.