Returns SplitGenerators.

def _split_generators(self, dl_manager):
    """Returns SplitGenerators."""
    path = dl_manager.manual_dir
    train_path = os.path.join(path, _TRAIN_DIR)
    val_path = os.path.join(path, _VALIDATION_DIR)

    if not tf.io.gfile.exists(train_path) or not tf.io.gfile.exists(val_path):
      msg = ("You must download the dataset folder from CheXpert"
             "website manually and place it into %s." % path)
      raise AssertionError(msg)

    return [
        tfds.core.SplitGenerator(
            name=tfds.Split.TRAIN,
            num_shards=100,
            gen_kwargs={
                "imgs_path": path,  # Relative img path is provided in csv
                "csv_path": os.path.join(path, _TRAIN_LABELS_FNAME)
            },
        ),
        tfds.core.SplitGenerator(
            name=tfds.Split.VALIDATION,
            num_shards=10,
            gen_kwargs={
                "imgs_path": path,
                "csv_path": os.path.join(path, _VALIDATION_LABELS_FNAME)
            },
        ),
    ]