code: def primitives(self):
          
          prim_molecules = [
              p.primitive for p in self._molecules if hasattr(p, 'primitive')]
          prim_assembly = Assembly(molecules=prim_molecules, assembly_id=self.id)
          return prim_assembly
docs: Generates a new `Assembly` containing the primitives of each Polymer.
  
          Notes
          -----
          Metadata is not currently preserved from the parent object.
  
          Returns
          -------
          prim_assembly : ampal.Protein
              `Assembly` containing only the primitives of the `Polymers`
              in the original `Assembly`.