docs: def get_monomers(self, ligands=True):
          """Retrieves all the `Monomers` from the AMPAL object.
  
          Parameters
          ----------
          ligands : bool, optional
              If true, will include ligand `Monomers`.
          """
          if ligands and self.ligands:
              monomers = self._monomers + self.ligands._monomers
          else:
              monomers = self._monomers
          return iter(monomers)