code: def filepattern(self, data_dir, mode, shard=None):
      
      path = os.path.join(data_dir, self.dataset_filename())
      shard_str = "-%05d" % shard if shard is not None else ""
      if mode == DatasetSplit.TRAIN:
        suffix = "train"
      elif mode in [DatasetSplit.EVAL, tf.estimator.ModeKeys.PREDICT]:
        suffix = "dev"
      else:
        assert mode == DatasetSplit.TEST
        suffix = "test"
  
      return "%s-%s%s*" % (path, suffix, shard_str)
docs: Get filepattern for data files for mode.
  
      Matches mode to a suffix.
      * DatasetSplit.TRAIN: train
      * DatasetSplit.EVAL: dev
      * DatasetSplit.TEST: test
      * tf.estimator.ModeKeys.PREDICT: dev
  
      Args:
        data_dir: str, data directory.
        mode: DatasetSplit
        shard: int, if provided, will only read data from the specified shard.
  
      Returns:
        filepattern str