code: def _rc_sdiff(self, src, *args):
          
          args = list_or_args(src, args)
          src_set = self.smembers(args.pop(0))
          if src_set is not set([]):
              for key in args:
                  src_set.difference_update(self.smembers(key))
          return src_set
docs: Returns the members of the set resulting from the difference between
          the first set and all the successive sets.