docs: def _format_int(format, subtype, endian):
      """Return numeric ID for given format|subtype|endian combo."""
      result = _check_format(format)
      if subtype is None:
          subtype = default_subtype(format)
          if subtype is None:
              raise TypeError(
                  "No default subtype for major format {0!r}".format(format))
      elif not isinstance(subtype, (_unicode, str)):
          raise TypeError("Invalid subtype: {0!r}".format(subtype))
      try:
          result |= _subtypes[subtype.upper()]
      except KeyError:
          raise ValueError("Unknown subtype: {0!r}".format(subtype))
      if endian is None:
          endian = 'FILE'
      elif not isinstance(endian, (_unicode, str)):
          raise TypeError("Invalid endian-ness: {0!r}".format(endian))
      try:
          result |= _endians[endian.upper()]
      except KeyError:
          raise ValueError("Unknown endian-ness: {0!r}".format(endian))
  
      info = _ffi.new("SF_INFO*")
      info.format = result
      info.channels = 1
      if _snd.sf_format_check(info) == _snd.SF_FALSE:
          raise ValueError(
              "Invalid combination of format, subtype and endian")
      return result