code: async def hmset(self, name, mapping):
          
          if not mapping:
              raise DataError("'hmset' with 'mapping' of length 0")
          items = []
          for pair in iteritems(mapping):
              items.extend(pair)
          return await self.execute_command('HMSET', name, *items)
docs: Set key to value within hash ``name`` for each corresponding
          key and value from the ``mapping`` dict.