How to use the cltk.tag.pos.POSTag function in cltk

"""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]

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]

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]

def _get_pos_tags(self, tokens):
        """Iterate through list of tokens and use POS tagger to build
        a corresponding list of tags.

        :param tokens: List of tokens to be POS-tagged
        :return: List with POS-tag for each token
        """
        # Import (and define tagger) with other imports?    
        from cltk.tag.pos import POSTag
        tagger = POSTag('latin')
        tokens = " ".join(tokens)
        tags = tagger.tag_ngram_123_backoff(tokens)
        tags = [tag[1][0].lower() if tag[1] else tag[1] for tag in tags]
        return tags

def __init__(self):
        self.syllabifier = Syllabifier(language="old_norse_ipa")
        self.tr = Transcriber(DIPHTHONGS_IPA, DIPHTHONGS_IPA_class, IPA_class, old_norse_rules)
        self.tagger = POSTag('old_norse')