Loads a text file, and turns each line into an encoded sequence.

def build_dataset(filename, max_lines=-1):
    """Loads a text file, and turns each line into an encoded sequence."""
    encodings = dict(list(map(reversed, enumerate(string.printable))))
    digitize = lambda char: encodings[char] if char in encodings else len(encodings)
    encode_line = lambda line: np.array(list(map(digitize, line)))
    nonblank_line = lambda line: len(line) > 2

    with open(filename) as f:
        lines = f.readlines()

    encoded_lines = list(map(encode_line, list(filter(nonblank_line, lines))[:max_lines]))
    num_outputs = len(encodings) + 1

    return encoded_lines, num_outputs