code: def sunionstore(self, dest, keys, *args):
          
          keys = [self.redis_key(k) for k in self._parse_values(keys, args)]
          with self.pipe as pipe:
              return pipe.sunionstore(self.redis_key(dest), *keys)
docs: Store the union of sets specified by ``keys`` into a new
          set named ``dest``.  Returns the number of members in the new set.