Read DAVID Chart file. Store each line in a namedtuple.

def get_nts(self, fin_davidchart):
        """Read DAVID Chart file. Store each line in a namedtuple."""
        nts = []
        with open(fin_davidchart) as ifstrm:
            hdr_seen = False
            for line in ifstrm:
                line = line.rstrip()
                flds = line.split('\t')
                if hdr_seen:
                    ntd = self._init_nt(flds)
                    nts.append(ntd)
                else:
                    if line[:8] == 'Category':
                        assert len(flds) == 13, len(flds)
                        hdr_seen = True

            sys.stdout.write("  READ {N:5} GO IDs from DAVID Chart: {TSV}\n".format(
                N=len(nts), TSV=fin_davidchart))
        return nts