Lib/ctypes/_endian.py

   1 ######################################################################
   2 #  This file should be kept compatible with Python 2.3, see PEP 291. #
   3 ######################################################################
   4 import sys
   5 from ctypes import *
   6
   7 _array_type = type(c_int * 3)
   8
   9 def _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
  22 class _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
  40 if 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
  50 elif 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
  59 else:
  60     raise RuntimeError("Invalid byteorder")