Take in a dialogue (a sequence of tokenized utterances) and transform it into a
        sequence of sequences of indices

def vectorize_dialogue(self, dialogue, safe=True):
        """
        Take in a dialogue (a sequence of tokenized utterances) and transform it into a
        sequence of sequences of indices
        """
        if safe:
            return vectorize_dialogue_safe(dialogue)
        else:
            return vectorize_dialogue_unsafe(dialogue)