code: def update_refobj(self, old, new, reftrack):
          
          if old:
              del self._parentsearchdict[old]
          if new:
              self._parentsearchdict[new] = reftrack
docs: Update the parent search dict so that the reftrack can be found
          with the new refobj and delete the entry for the old refobj.
  
          Old or new can also be None.
  
          :param old: the old refobj of reftrack
          :param new: the new refobj of reftrack
          :param reftrack: The reftrack, which refobj was updated
          :type reftrack: :class:`Reftrack`
          :returns: None
          :rtype: None
          :raises: None