docs: def available_subtypes(format=None):
      """Return a dictionary of available subtypes.
  
      Parameters
      ----------
      format : str
          If given, only compatible subtypes are returned.
  
      Examples
      --------
      >>> import soundfile as sf
      >>> sf.available_subtypes('FLAC')
      {'PCM_24': 'Signed 24 bit PCM',
       'PCM_16': 'Signed 16 bit PCM',
       'PCM_S8': 'Signed 8 bit PCM'}
  
      """
      subtypes = _available_formats_helper(_snd.SFC_GET_FORMAT_SUBTYPE_COUNT,
                                           _snd.SFC_GET_FORMAT_SUBTYPE)
      return dict((subtype, name) for subtype, name in subtypes
                  if format is None or check_format(format, subtype))