def get_polypeptide_within(self, chain_id, resnum, angstroms, only_protein=True,
                               use_ca=False, custom_coord=None, return_resnums=False):
        """Get a Polypeptide object of the amino acids within X angstroms of the specified chain + residue number.

        Args:
            resnum (int): Residue number of the structure
            chain_id (str): Chain ID of the residue number
            angstroms (float): Radius of the search sphere
            only_protein (bool): If only protein atoms (no HETATMS) should be included in the returned sequence
            use_ca (bool): If the alpha-carbon atom should be used for searching, default is False (last atom of residue used)
            custom_coord (list): custom XYZ coord
            return_resnums (bool): if list of resnums should be returned

        Returns:
            Bio.PDB.Polypeptide.Polypeptide: Biopython Polypeptide object

        """
        # XTODO: documentation, unit test
        if self.structure:
            parsed = self.structure
        else:
            parsed = self.parse_structure()

        residue_list = ssbio.protein.structure.properties.residues.within(resnum=resnum, chain_id=chain_id,
                                                                          model=parsed.first_model,
                                                                          angstroms=angstroms, use_ca=use_ca,
                                                                          custom_coord=custom_coord)

        if only_protein:
            filtered_residue_list = [x for x in residue_list if x.id[0] == ' ']
        else:
            filtered_residue_list = residue_list

        residue_list_combined = Polypeptide(filtered_residue_list)

        if return_resnums:
            resnums = [int(x.id[1]) for x in filtered_residue_list]
            return residue_list_combined, resnums

        return residue_list_combined
Get a Polypeptide object of the amino acids within X angstroms of the specified chain + residue number.

        Args:
            resnum (int): Residue number of the structure
            chain_id (str): Chain ID of the residue number
            angstroms (float): Radius of the search sphere
            only_protein (bool): If only protein atoms (no HETATMS) should be included in the returned sequence
            use_ca (bool): If the alpha-carbon atom should be used for searching, default is False (last atom of residue used)
            custom_coord (list): custom XYZ coord
            return_resnums (bool): if list of resnums should be returned

        Returns:
            Bio.PDB.Polypeptide.Polypeptide: Biopython Polypeptide object