def _retrieve_tag(self, text):
        """Tag text with chosen tagger and clean tags.

        Tag format: [('word', 'tag')]

        :param text: string
        :return: list of tuples, with each tuple containing the word and its pos tag
        :rtype : list
        """
        if self.tagger == 'tag_ngram_123_backoff':  # Data format: Perseus Style (see https://github.com/cltk/latin_treebank_perseus)
            tags = POSTag('latin').tag_ngram_123_backoff(text.lower())
            return [(tag[0], tag[1]) for tag in tags]
        elif self.tagger == 'tag_tnt':
            tags = POSTag('latin').tag_tnt(text.lower())
            return [(tag[0], tag[1]) for tag in tags]
        elif self.tagger == 'tag_crf':
            tags = POSTag('latin').tag_crf(text.lower())
            return [(tag[0], tag[1]) for tag in tags]
Tag text with chosen tagger and clean tags.

        Tag format: [('word', 'tag')]

        :param text: string
        :return: list of tuples, with each tuple containing the word and its pos tag
        :rtype : list