Create a gene product to GO set dict.

def get_gene2gos(go2nt):
        """Create a gene product to GO set dict."""
        gene2gos = cx.defaultdict(set)
        nt0 = next(iter(go2nt.values()))
        b_str = isinstance(nt0.study_items, str)
        # print("NNNNTTTT", nt0)
        for goid, ntgo in go2nt.items():
            study_items = ntgo.study_items.split(', ') if b_str else ntgo.study_items
            for geneid in study_items:
                gene2gos[geneid].add(goid)
        if b_str:
          b_set = set(isinstance(g.isdigit(), int) for g in nt0.study_items.split(', '))
          if b_set == set([True]):
            return {int(g):gos for g, gos in gene2gos.items()}
        return {g:gos for g, gos in gene2gos.items()}