code: def numbered_syllable_to_accented(s):
      
      if s == 'r5':
          return 'r'  # Special case for 'r' suffix.
  
      lowercase_syllable, case_memory = _lower_case(s)
      syllable, tone = _parse_numbered_syllable(lowercase_syllable)
      syllable = syllable.replace('v', '\u00fc')
      if re.search('[%s]' % _UNACCENTED_VOWELS, syllable) is None:
          return s
      if 'a' in syllable:
          accented_a = _numbered_vowel_to_accented('a', tone)
          accented_syllable = syllable.replace('a', accented_a)
      elif 'e' in syllable:
          accented_e = _numbered_vowel_to_accented('e', tone)
          accented_syllable = syllable.replace('e', accented_e)
      elif 'o' in syllable:
          accented_o = _numbered_vowel_to_accented('o', tone)
          accented_syllable = syllable.replace('o', accented_o)
      else:
          vowel = syllable[max(map(syllable.rfind, _UNACCENTED_VOWELS))]
          accented_vowel = _numbered_vowel_to_accented(vowel, tone)
          accented_syllable = syllable.replace(vowel, accented_vowel)
      return _restore_case(accented_syllable, case_memory)
docs: Convert numbered Pinyin syllable *s* to an accented Pinyin syllable.
  
      It implements the following algorithm to determine where to place tone
      marks:
  
      1. If the syllable has an 'a', 'e', or 'o' (in that order), put the
          tone mark over that vowel.
      2. Otherwise, put the tone mark on the last vowel.