Splits of data to produce and number of output shards for each.

def dataset_splits(self):
    """Splits of data to produce and number of output shards for each."""
    return [{
        "split": problem.DatasetSplit.TRAIN,
        "shards": _TRAIN_SHARDS,
    }, {
        "split": problem.DatasetSplit.EVAL,
        "shards": _DEV_SHARDS,
    }]