Return ordered dict for group to namedtuple

def get_grp2code2nt(self):
        """Return ordered dict for group to namedtuple"""
        grp2code2nt = cx.OrderedDict([(g, []) for g in self.grps])
        for code, ntd in self.code2nt.items():
            grp2code2nt[ntd.group].append((code, ntd))
        for grp, nts in grp2code2nt.items():
            grp2code2nt[grp] = cx.OrderedDict(nts)
        return grp2code2nt