def create_group(self, **kwargs: Any) -> Self:
        """Create a group.

        This assumes that :meth:`~lightning.fabric.plugins.collectives.Collective.init_group` has been
        called already by the user.

        """
        if self._group is not None:
            raise RuntimeError(f"`{type(self).__name__}` already owns a group.")
        self._group = self.new_group(**kwargs)
        return self
Create a group.

        This assumes that :meth:`~lightning.fabric.plugins.collectives.Collective.init_group` has been
        called already by the user.

        
src/lightning/fabric/plugins/collectives/collective.py