Get keyword args for a GoSubDag.

def _get_kwsdag(self, goids, go2obj, **kws_all):
        """Get keyword args for a GoSubDag."""
        kws_dag = {}
        # Term Counts for GO Term information score
        tcntobj = self._get_tcntobj(goids, go2obj, **kws_all)  # TermCounts or None
        if tcntobj is not None:
            kws_dag['tcntobj'] = tcntobj
        # GO letters specified by the user
        if 'go_aliases' in kws_all:
            fin_go_aliases = kws_all['go_aliases']
            if os.path.exists(fin_go_aliases):
                go2letter = read_d1_letter(fin_go_aliases)
                if go2letter:
                    kws_dag['go2letter'] = go2letter
        return kws_dag