Add a namedtuple field of type string generated from an existing namedtuple field.

def add_f2str(self, dcts, srcfld, dstfld, dstfmt):
        """Add a namedtuple field of type string generated from an existing namedtuple field."""
        # Example: f2str = objntmgr.add_f2str(dcts, "p_fdr_bh", "s_fdr_bh", "{:8.2e}")
        # ntobj = self.get_ntobj()
        # print(ntobj)
        assert len(dcts) == len(self.nts)
        for dct, ntgoea in zip(dcts, self.nts):
            valorig = getattr(ntgoea, srcfld)
            valstr = dstfmt.format(valorig)
            dct[dstfld] = valstr