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

def filepattern(self, data_dir, mode, shard=None):
    """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
    """
    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)