code: def _parse_zhuyin_syllable(unparsed_syllable):
      
      zhuyin_tone = unparsed_syllable[-1]
      if zhuyin_tone in zhon.zhuyin.characters:
          syllable, tone = unparsed_syllable, '1'
      elif zhuyin_tone in zhon.zhuyin.marks:
          for tone_number, tone_mark in _ZHUYIN_TONES.items():
              if zhuyin_tone == tone_mark:
                  syllable, tone = unparsed_syllable[:-1], tone_number
      else:
          raise ValueError("Invalid syllable: %s" % unparsed_syllable)
  
      return syllable, tone
docs: Return the syllable and tone of a Zhuyin syllable.