code: def use_size(self):
          "Return the total used size, including children."
          if self._nodes is None:
              return self._use_size
          return sum(i.use_size() for i in self._nodesf use_size(self):
          "Return the total used size, including children."
          if self._nodes is None:
              return self._use_size
          return sum(i.use_size() for i in self._nodes)
docs: Return the total used size, including children.