code: def helices(self):
          
          hel_molecules = list(itertools.chain(
              *[p.helices._molecules
                for p in self._molecules if hasattr(p, 'helices')]))
          hel_assembly = Assembly(molecules=hel_molecules, assembly_id=self.id)
          return hel_assembly
docs: Generates new `Assembly` containing just α-helices.
  
          Notes
          -----
          Metadata is not currently preserved from the parent object.
  
          Returns
          -------
          hel_assembly : ampal.Protein
              `Assembly` containing only the α-helices of the original `Assembly`.