def get_char_vocab(dataset):
    """Build char vocabulary from an iterable of datasets objects

    Args:
        dataset: a iterator yielding tuples (sentence, tags)

    Returns:
        a set of all the characters in the dataset

    """
    vocab_char = set()
    for words, _ in dataset:
        for word in words:
            vocab_char.update(word)
    return vocab_char
