code: def resolvePrefix(self):
          
          tmpstrlist = []
          tmpstodict = {}
          for line in self.file_lines:
              if line.startswith('%'):
                  stolist = line.replace('%', '').split('sto')
                  rpnexp = stolist[0].strip()  # rpn expression
                  rpnvar = stolist[1].strip()  # rpn variable
                  tmpstodict[rpnvar] = rpnexp
                  # bug: rpnval in rpnexp
                  # raises error when converting string convert to float
                  # Found: 2016-06-08 22:29:25 PM CST
                  # Fixed: 2016-06-12 11:51:01 AM CST
                  # e.g.
                  # a sto 0.1
                  # a sto b
                  # then b should be 0.1,
                  # i.e. b -> a -> 0.1
                  # solve the 'sto chain' assignment issue.
  
          self.stodict = self.resolve_rpn(tmpstodict)
          for k, v in self.stodict.items():
              stostr = '% {val} sto {var}'.format(val=v, var=k)
              tmpstrlist.append(stostr)
          self.prestrdict['_prefixstr'] = tmpstrlist
docs: extract prefix information into dict with the key of '_prefixstr'