code: def _get_layer(self, layer_id):
          
          if layer_id not in self._layer_id_to_layer:
              self._svg.setdefault("g", [])
              layer = {
                  "g": [],
                  "@inkscape:label": layer_id,
                  "@id": layer_id,
                  "@inkscape:groupmode": "layer",
                  "@class": "row"
              }
              self._layer_id_to_layer[layer_id] = layer
              self._svg["g"].append(layer)
          return self._layer_id_to_layer[layer_id]
docs: :return: the layer with the :paramref:`layer_id`. If the layer
            does not exist, it is created.
          :param str layer_id: the id of the layer