code: def _parse_numbered_syllable(unparsed_syllable):
      
      tone_number = unparsed_syllable[-1]
      if not tone_number.isdigit():
          syllable, tone = unparsed_syllable, '5'
      elif tone_number == '0':
          syllable, tone = unparsed_syllable[:-1], '5'
      elif tone_number in '12345':
          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 numbered Pinyin syllable.