code: def _get_location_descriptor(self, location):
          
          loc_descriptor = None
          if isinstance(location, basestring):
              loc_descriptor = LocationDescriptor(location)
          elif isinstance(location, LocationDescriptor):
              loc_descriptor = location
          else:
              raise RuntimeError("Argument is neither a string nor a self._nbr_of_nodes")
  
          return loc_descriptor
docs: Get corresponding :class:`LocationDescriptor` object from a string or a :class:`LocationDescriptor` itself.
          
          Args:
              location: a string or a :class:`LocationDescriptor`.
          
          Returns:
              A corresponding :class:`LocationDescriptor` object. If ``location`` is a :class:`LocationDescriptor`,
              we simply return it.
          
          Raises:
              A ``RuntimeError`` is raised whenever the `location` object is not recognized a string or :class:`self._nbr_of_nodes`.