import random


def split_dataset(dataset, num_train=1200):
    """
    Split the dataset into a training and test set.

    Args:
      dataset: an iterable of Characters.

    Returns:
      A tuple (train, test) of Character sequences.
    """
    all_data = list(dataset)
    random.shuffle(all_data)
    return all_data[:num_train], all_data[num_train:]