import tensorflow as tf

        "targets": tf.FixedLenFeature([1], tf.int64),
    }
    data_items_to_decoders = None
    return (data_fields, data_items_to_decoders)


def txt_line_iterator(txt_path):
  """Iterate through lines of file."""
  with tf.gfile.Open(txt_path) as f:
    for line in f:
      yield line.strip()


def text2text_txt_iterator(source_txt_path, target_txt_path):
  """Yield dicts for Text2TextProblem.generate_samples from lines of files."""
  for inputs, targets in zip(
