docs: def mset(self, args):
          """
          mset wrapper that batches keys per shard and execute as few
          msets as necessary to set the keys in all the shards involved.
  
          This method should be invoked on a TwemRedis instance as if it
          were being invoked directly on a StrictRedis instance.
          """
          key_map = collections.defaultdict(dict)
          result_count = 0
          for key in args.keys():
              value = args[key]
              shard_num = self.get_shard_num_by_key(key)
              key_map[shard_num][key] = value
  
          # TODO: parallelize
          for shard_num in key_map.keys():
              shard = self.get_shard_by_num(shard_num)
              result_count += shard.mset(key_map[shard_num])
  
          return result_count