code: def rinse_rpnexp(self, rpnexp, rpndict):
          
          for wd in rpnexp.split():
              if wd in rpndict:
                  try:
                      val = float(rpndict[wd])
                      rpnexp = rpnexp.replace(wd, str(val))
                  except:
                      pass
          return rpnexp
docs: replace valid keyword of rpnexp from rpndict
              e.g. rpnexp = 'b a /', rpndict = {'b': 10}
              then after rinsing, rpnexp = '10 a /'
  
              return rinsed rpnexp