I should have included the failures in my first message, sorry about that.

IIRC the workaround in PyObjC I mention in my initial message does explicit sign extension when needed.

W.r.t to the first couple of failures, not that:

   struct.unpack('b', struct.pack('B', 130)) == (-126,)



======================================================================
FAIL: test_byte (ctypes.test.test_cfuncs.CFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/PythonDev.framework/Versions/2.7/lib/python2.7/ctypes/test/test_cfuncs.py", line 21, in test_byte
    self.assertEqual(self.S(), -126)
AssertionError: 130 != -126

======================================================================
FAIL: test_byte_plus (ctypes.test.test_cfuncs.CFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/PythonDev.framework/Versions/2.7/lib/python2.7/ctypes/test/test_cfuncs.py", line 27, in test_byte_plus
    self.assertEqual(self.S(), -126)
AssertionError: 130 != -126

======================================================================
FAIL: test_short (ctypes.test.test_cfuncs.CFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/PythonDev.framework/Versions/2.7/lib/python2.7/ctypes/test/test_cfuncs.py", line 45, in test_short
    self.assertEqual(self.S(), -32766)
AssertionError: 32770 != -32766

======================================================================
FAIL: test_short_plus (ctypes.test.test_cfuncs.CFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/PythonDev.framework/Versions/2.7/lib/python2.7/ctypes/test/test_cfuncs.py", line 51, in test_short_plus
    self.assertEqual(self.S(), -32766)
AssertionError: 32770 != -32766

======================================================================
FAIL: test_doubleresult (ctypes.test.test_functions.FunctionTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/PythonDev.framework/Versions/2.7/lib/python2.7/ctypes/test/test_functions.py", line 143, in test_doubleresult
    self.assertEqual(result, -21)
AssertionError: 65771.0 != -21

======================================================================
FAIL: test_floatresult (ctypes.test.test_functions.FunctionTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/PythonDev.framework/Versions/2.7/lib/python2.7/ctypes/test/test_functions.py", line 131, in test_floatresult
    self.assertEqual(result, -21)
AssertionError: 65771.0 != -21

======================================================================
FAIL: test_intresult (ctypes.test.test_functions.FunctionTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/PythonDev.framework/Versions/2.7/lib/python2.7/ctypes/test/test_functions.py", line 105, in test_intresult
    self.assertEqual(result, -21)
AssertionError: 65771 != -21

======================================================================
FAIL: test_longdoubleresult (ctypes.test.test_functions.FunctionTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/PythonDev.framework/Versions/2.7/lib/python2.7/ctypes/test/test_functions.py", line 155, in test_longdoubleresult
    self.assertEqual(result, -21)
AssertionError: 65771.0 != -21