update rpndict, try to solve rpn expressions as many as possible,
            leave unsolvable unchanged.

            return new dict

def update_rpndict(self, rpndict):
        """ update rpndict, try to solve rpn expressions as many as possible,
            leave unsolvable unchanged.

            return new dict
        """
        tmpdict = {k: v for k, v in rpndict.items()}
        for k, v in rpndict.items():
            v_str = str(v)
            if rpn.Rpn.solve_rpn(v_str) is None:
                tmpdict[k] = self.rinse_rpnexp(v_str, tmpdict)
            else:
                tmpdict[k] = rpn.Rpn.solve_rpn(v_str)
        return tmpdict