eryksun added the comment:
A functional memoryview for ctypes objects would avoid having to use
workarounds, such as the following:
>>> d = ctypes.c_double()
>>> b = (ctypes.c_char * ctypes.sizeof(d)).from_buffer(d)
>>> b[:] = b'abcdefgh'
>>> d.value
8.540883223036124e+194
or using numpy.frombuffer as a bridge:
>>> d = ctypes.c_double()
>>> m = memoryview(numpy.frombuffer(d, 'B'))
>>> m[:] = b'abcdefgh'
>>> d.value
8.540883223036124e+194
David's request that cast('B') should be made to work for all contiguous
buffers seems reasonable. That said, the ctypes format strings also need
fixing. Let's see what happens when "@d" is used instead of "<d":
>>> double_stgdict = stgdict(ctypes.c_double)
>>> double_stgdict
dict:
ob_base:
ob_refcnt: 1
ob_type: py_object(<class 'StgDict'>)
ma_used: 7
ma_keys: LP_PyDictKeysObject(0x1aa5750)
ma_values: LP_LP_PyObject(<NULL>)
size: 8
align: 8
length: 0
ffi_type_pointer:
size: 8
alignment: 8
type: 3
elements: <NULL>
proto: py_object('d')
setfunc: SETFUNC(0x7f9f9b6e3e60)
getfunc: GETFUNC(0x7f9f9b6e3d90)
paramfunc: PARAMFUNC(0x7f9f9b6e31d0)
argtypes: py_object(<NULL>)
converters: py_object(<NULL>)
restype: py_object(<NULL>)
checker: py_object(<NULL>)
flags: 4096
format: b'<d'
ndim: 0
shape: LP_c_long(<NULL>)
>>> double_stgdict.format = b'@d'
>>> d = ctypes.c_double(3.14)
>>> m = memoryview(d)
>>> m[()]
3.14
>>> m[()] = 6.28
>>> d.value
6.28
>>> m = m.cast('B')
>>> m[:] = b'abcdefgh'
>>> d.value
8.540883223036124e+194
This shows that changing the format string (set by PyCSimpleType_new in
_ctypes.c) to use "@" makes the memoryview work normally. OTOH, the swapped
type (e.g. c_double.__ctype_be__) would need to continue to use a standard
little-endian ("<") or big-endian (">") format.
----------
nosy: +eryksun
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue15944>
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