import sys from ctypes import * _array_type = type(Array) def _other_endian(typ): """Return the type with the 'other' byte order. Simple types like c_int and so on already have __ctype_be__ and __ctype_le__ attributes which contain the types, for more complicated types arrays and structures are supported. """ # check _OTHER_ENDIAN attribute (present if typ is primitive type) if hasattr(typ, _OTHER_ENDIAN): return getattr(typ, _OTHER_ENDIAN) # if typ is array if isinstance(typ, _array_type): return _other_endian(typ._type_) * typ._length_ # if typ is structure if issubclass(typ, Structure): return typ raise TypeError("This type does not support other endian: %s" % typ) class _swapped_meta(type(Structure)): def __setattr__(self, attrname, value): if attrname == "_fields_": fields = [] for desc in value: name = desc[0] typ = desc[1] rest = desc[2:] fields.append((name, _other_endian(typ)) + rest) value = fields super().__setattr__(attrname, value) ################################################################ # Note: The Structure metaclass checks for the *presence* (not the # value!) of a _swapped_bytes_ attribute to determine the bit order in # structures containing bit fields. if sys.byteorder == "little": _OTHER_ENDIAN = "__ctype_be__" LittleEndianStructure = Structure class BigEndianStructure(Structure, metaclass=_swapped_meta): """Structure with big endian byte order""" __slots__ = () _swappedbytes_ = None elif sys.byteorder == "big": _OTHER_ENDIAN = "__ctype_le__" BigEndianStructure = Structure class LittleEndianStructure(Structure, metaclass=_swapped_meta): """Structure with little endian byte order""" __slots__ = () _swappedbytes_ = None else: raise RuntimeError("Invalid byteorder")