Get a list of namedtuples, one for each annotation.

def _init_w_godag(self):
        """Get a list of namedtuples, one for each annotation."""
        nts = []
        ntobj = cx.namedtuple('ntanno', self.flds + ['NS'])
        for itemid, gos in self.id2gos.items():
            for goid in gos:
                goobj = self.godag.get(goid, '')
                nts.append(ntobj(
                    DB_ID=itemid,
                    GO_ID=goid,
                    NS=NAMESPACE2NS[goobj.namespace] if goobj else ''))
        return nts