':return: list of (sent_index, word_indices) tuples'

def _sent_and_word_indices(self, indices):

    sent_indices = set((((i / 1000) - 1) for i in indices if (i >= 0)))
    if sent_indices:
        pairs = []
        for sent_index in sent_indices:
            word_indices = [((i % 1000) - 1) for i in indices if (sent_index == ((i / 1000) - 1))]
            pairs.append((sent_index, word_indices))
        return pairs
    else:
        word_indices = [((i % 1000) - 1) for i in indices]
        return [(None, word_indices)]
