Returns a list of residues in pdb_name which differ from the pdbs corresponding to the names in pdb_list.

def get_differing_atom_residue_ids(self, pdb_name, pdb_list):
        '''Returns a list of residues in pdb_name which differ from the pdbs corresponding to the names in pdb_list.'''

        assert(pdb_name in self.pdb_names)
        assert(set(pdb_list).intersection(set(self.pdb_names)) == set(pdb_list)) # the names in pdb_list must be in pdb_names

        differing_atom_residue_ids = set()
        for other_pdb in pdb_list:
            differing_atom_residue_ids = differing_atom_residue_ids.union(set(self.differing_atom_residue_ids[(pdb_name, other_pdb)]))

        return sorted(differing_atom_residue_ids)