/Lib/ctypes/_endian.py

 1######################################################################
 2#  This file should be kept compatible with Python 2.3, see PEP 291. #
 3######################################################################
 4import sys
 5from ctypes import *
 6
 7_array_type = type(c_int * 3)
 8
 9def _other_endian(typ):
10    """Return the type with the 'other' byte order.  Simple types like
11    c_int and so on already have __ctype_be__ and __ctype_le__
12    attributes which contain the types, for more complicated types
13    only arrays are supported.
14    """
15    try:
16        return getattr(typ, _OTHER_ENDIAN)
17    except AttributeError:
18        if type(typ) == _array_type:
19            return _other_endian(typ._type_) * typ._length_
20        raise TypeError("This type does not support other endian: %s" % typ)
21
22class _swapped_meta(type(Structure)):
23    def __setattr__(self, attrname, value):
24        if attrname == "_fields_":
25            fields = []
26            for desc in value:
27                name = desc[0]
28                typ = desc[1]
29                rest = desc[2:]
30                fields.append((name, _other_endian(typ)) + rest)
31            value = fields
32        super(_swapped_meta, self).__setattr__(attrname, value)
33
34################################################################
35
36# Note: The Structure metaclass checks for the *presence* (not the
37# value!) of a _swapped_bytes_ attribute to determine the bit order in
38# structures containing bit fields.
39
40if sys.byteorder == "little":
41    _OTHER_ENDIAN = "__ctype_be__"
42
43    LittleEndianStructure = Structure
44
45    class BigEndianStructure(Structure):
46        """Structure with big endian byte order"""
47        __metaclass__ = _swapped_meta
48        _swappedbytes_ = None
49
50elif sys.byteorder == "big":
51    _OTHER_ENDIAN = "__ctype_le__"
52
53    BigEndianStructure = Structure
54    class LittleEndianStructure(Structure):
55        """Structure with little endian byte order"""
56        __metaclass__ = _swapped_meta
57        _swappedbytes_ = None
58
59else:
60    raise RuntimeError("Invalid byteorder")