def visible_object_layers(self):
        """ This must return layer objects

        This is not required for custom data formats.

        :return: Sequence of pytmx object layers/groups
        """
        return (layer for layer in self.tmx.visible_layers
                if isinstance(layer, pytmx.TiledObjectGroup))
This must return layer objects

        This is not required for custom data formats.

        :return: Sequence of pytmx object layers/groups