code: def sort(self, key=None, reverse=False):
          
          self._sites.sort(key=key, reverse=reverse)
docs: Sort a structure in place. The parameters have the same meaning as in
          list.sort. By default, sites are sorted by the electronegativity of
          the species. The difference between this method and
          get_sorted_structure (which also works in IStructure) is that the
          latter returns a new Structure, while this just sorts the Structure
          in place.
  
          Args:
              key: Specifies a function of one argument that is used to extract
                  a comparison key from each list element: key=str.lower. The
                  default value is None (compare the elements directly).
              reverse (bool): If set to True, then the list elements are sorted
                  as if each comparison were reversed.