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      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(Array)
      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     arrays and structures are supported.
     14     """
     15     # check _OTHER_ENDIAN attribute (present if typ is primitive type)
     16     if hasattr(typ, _OTHER_ENDIAN):
     17         return getattr(typ, _OTHER_ENDIAN)
     18     # if typ is array
     19     if isinstance(typ, _array_type):
     20         return _other_endian(typ._type_) * typ._length_
     21     # if typ is structure
     22     if issubclass(typ, Structure):
     23         return typ
     24     raise TypeError("This type does not support other endian: %s" % typ)
     25 
     26 class _swapped_meta(type(Structure)):
     27     def __setattr__(self, attrname, value):
     28         if attrname == "_fields_":
     29             fields = []
     30             for desc in value:
     31                 name = desc[0]
     32                 typ = desc[1]
     33                 rest = desc[2:]
     34                 fields.append((name, _other_endian(typ)) + rest)
     35             value = fields
     36         super(_swapped_meta, self).__setattr__(attrname, value)
     37 
     38 ################################################################
     39 
     40 # Note: The Structure metaclass checks for the *presence* (not the
     41 # value!) of a _swapped_bytes_ attribute to determine the bit order in
     42 # structures containing bit fields.
     43 
     44 if sys.byteorder == "little":
     45     _OTHER_ENDIAN = "__ctype_be__"
     46 
     47     LittleEndianStructure = Structure
     48 
     49     class BigEndianStructure(Structure):
     50         """Structure with big endian byte order"""
     51         __metaclass__ = _swapped_meta
     52         _swappedbytes_ = None
     53 
     54 elif sys.byteorder == "big":
     55     _OTHER_ENDIAN = "__ctype_le__"
     56 
     57     BigEndianStructure = Structure
     58     class LittleEndianStructure(Structure):
     59         """Structure with little endian byte order"""
     60         __metaclass__ = _swapped_meta
     61         _swappedbytes_ = None
     62 
     63 else:
     64     raise RuntimeError("Invalid byteorder")
     65