def _tagtype_lookup(self, tag):
        for test_tag, key in self.tagtype_map.items():
            # Match case-insensitively.
            if test_tag.lower() == tag.lower():
                return test_tag, key
        raise BPDError(ERROR_UNKNOWN, u'no such tagtype')
Uses `tagtype_map` to look up the beets column name for an
dataset/ETHPy150Open beetbox/beets/beetsplug/bpd/__init__.py/Server._tagtype_lookup