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bpo-32782: PEP3118 itemsize of an empty ctypes array should not be 0 #5576

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bpo-32782: PEP3118 itemsize of an empty ctypes array should not be 0 #5576

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f4e3ca9
bpo-32782: PEP3118 itemsize of an empty ctypes array should not be 0
eric-wieser Feb 7, 2018
dd2069f
bpo-32782: Avoid touching python attributes when the C attribute is a…
eric-wieser Jun 7, 2019
0cabf5d
Merge remote-tracking branch 'upstream/main' into ctypes-empty-array-…
eric-wieser Jul 7, 2022
d459459
Merge remote-tracking branch 'upstream/main' into ctypes-empty-array-…
eric-wieser Dec 15, 2022
accc969
Merge branch 'main' into ctypes-empty-array-itemsize
eric-wieser Dec 15, 2022
ff4dd22
Merge branch 'main' into ctypes-empty-array-itemsize
eric-wieser Dec 22, 2022
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2 Lib/test/test_ctypes/test_pep3118.py
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@@ -176,7 +176,9 @@ class Complete(Structure):
## arrays and pointers

(c_double * 4, "<d", (4,), c_double),
(c_double * 0, "<d", (0,), c_double),
(c_float * 4 * 3 * 2, "<f", (2,3,4), c_float),
(c_float * 4 * 0 * 2, "<f", (2,0,4), c_float),
(POINTER(c_short) * 2, "&<" + s_short, (2,), POINTER(c_short)),
(POINTER(c_short) * 2 * 3, "&<" + s_short, (3,2,), POINTER(c_short)),
(POINTER(c_short * 2), "&(2)<" + s_short, (), POINTER(c_short)),
3 Misc/NEWS.d/next/Core and Builtins/2018-02-06-23-21-13.bpo-32782.EJVSfR.rst
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@@ -0,0 +1,3 @@
``ctypes`` arrays of length 0 now report a correct itemsize when a
``memoryview`` is constructed from them, rather than always giving a value
of 0.
33 Modules/_ctypes/_ctypes.c
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@@ -2731,11 +2731,33 @@ static PyMemberDef PyCData_members[] = {
{ NULL },
};

static int PyCData_NewGetBuffer(PyObject *myself, Py_buffer *view, int flags)
/* Find the innermost type of an array type, returning a borrowed reference */
static PyObject *
PyCData_item_type(PyObject *type)
{
if (PyCArrayTypeObject_Check(type)) {
StgDictObject *stg_dict;
PyObject *elem_type;

/* asserts used here as these are all guaranteed by construction */
stg_dict = PyType_stgdict(type);
assert(stg_dict);
elem_type = stg_dict->proto;
assert(elem_type);
return PyCData_item_type(elem_type);
}
else {
return type;
}
}

static int
PyCData_NewGetBuffer(PyObject *myself, Py_buffer *view, int flags)
{
CDataObject *self = (CDataObject *)myself;
StgDictObject *dict = PyObject_stgdict(myself);
Py_ssize_t i;
PyObject *item_type = PyCData_item_type((PyObject*)Py_TYPE(myself));
StgDictObject *item_dict = PyType_stgdict(item_type);

if (view == NULL) return 0;

@@ -2747,12 +2769,7 @@ static int PyCData_NewGetBuffer(PyObject *myself, Py_buffer *view, int flags)
view->format = dict->format ? dict->format : "B";
view->ndim = dict->ndim;
view->shape = dict->shape;
view->itemsize = self->b_size;
if (view->itemsize) {
for (i = 0; i < view->ndim; ++i) {
view->itemsize /= dict->shape[i];
}
}
view->itemsize = item_dict->size;
view->strides = NULL;
view->suboffsets = NULL;
view->internal = NULL;