def decoder_inputs_and_outputs(target_words, base_vocab):
    """Convert a sequence of tokens into a decoder input seq and output seq.
    
    Args:
        target_words (list[unicode])
        base_vocab (Vocab)

    Returns:
        input_words (list[unicode])
        output_words (list[unicode])
    """
    # prepend with <start> token
    input_words = [base_vocab.START] + target_words
    # append with <stop> token
    output_words = target_words + [base_vocab.STOP]
    return input_words, output_words