Returns a new `Polypeptide` containing the `Residues` in start/end range.

        Parameters
        ----------
        start : str
            string representing start residue id (PDB numbering)
        end : str
            string representing end residue id (PDB numbering)

        Returns
        -------
        slice_polymer : Polymer
            Polymer containing the residue range specified by start-end

def get_slice_from_res_id(self, start, end):
        """Returns a new `Polypeptide` containing the `Residues` in start/end range.

        Parameters
        ----------
        start : str
            string representing start residue id (PDB numbering)
        end : str
            string representing end residue id (PDB numbering)

        Returns
        -------
        slice_polymer : Polymer
            Polymer containing the residue range specified by start-end
        """

        id_dict = {str(m.id): m for m in self._monomers}
        slice_polymer = Polypeptide(
            [id_dict[str(x)] for x in range(int(start), int(end) + 1)], self.id)
        return slice_polymer