Retrieves all the `Monomers` from the AMPAL object.

        Parameters
        ----------
        ligands : bool, optional
            If true, will include ligand `Monomers`.

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)