8000 gh-76963: PEP3118 itemsize of an empty ctypes array should not be 0 (… · python/cpython@84bc6a4 · GitHub
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gh-76963: PEP3118 itemsize of an empty ctypes array should not be 0 (GH-5576)
The itemsize returned in a memoryview of a ctypes array is now computed from the item type, instead of dividing the total size by the length and assuming that the length is not zero.
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+30
-8
lines changed

3 files changed

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‎Lib/test/test_ctypes/test_pep3118.py

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@@ -176,7 +176,9 @@ class Complete(Structure):
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## arrays and pointers
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(c_double * 4, "<d", (4,), c_double),
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(c_double * 0, "<d", (0,), c_double),
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(c_float * 4 * 3 * 2, "<f", (2,3,4), c_float),
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(c_float * 4 * 0 * 2, "<f", (2,0,4), c_float),
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(POINTER(c_short) * 2, "&<" + s_short, (2,), POINTER(c_short)),
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(POINTER(c_short) * 2 * 3, "&<" + s_short, (3,2,), POINTER(c_short)),
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(POINTER(c_short * 2), "&(2)<" + s_short, (), POINTER(c_short)),

‎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 @@
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``ctypes`` arrays of length 0 now report a correct itemsize when a
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``memoryview`` is constructed from them, rather than always giving a value
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of 0.

‎Modules/_ctypes/_ctypes.c

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@@ -2731,11 +2731,33 @@ static PyMemberDef PyCData_members[] = {
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{ NULL },
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};
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static int PyCData_NewGetBuffer(PyObject *myself, Py_buffer *view, int flags)
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/* Find the innermost type of an array type, returning a borrowed reference */
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static PyObject *
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PyCData_item_type(PyObject *type)
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{
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if (PyCArrayTypeObject_Check(type)) {
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StgDictObject *stg_dict;
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PyObject *elem_type;
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/* asserts used here as these are all guaranteed by construction */
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stg_dict = PyType_stgdict(type);
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assert(stg_dict);
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elem_type = stg_dict->proto;
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assert(elem_type);
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return PyCData_item_type(elem_type);
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}
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else {
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return type;
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}
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}
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static int
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PyCData_NewGetBuffer(PyObject *myself, Py_buffer *view, int flags)
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{
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CDataObject *self = (CDataObject *)myself;
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StgDictObject *dict = PyObject_stgdict(myself);
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Py_ssize_t i;
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PyObject *item_type = PyCData_item_type((PyObject*)Py_TYPE(myself));
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StgDictObject *item_dict = PyType_stgdict(item_type);
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if (view == NULL) return 0;
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@@ -2747,12 +2769,7 @@ static int PyCData_NewGetBuffer(PyObject *myself, Py_buffer *view, int flags)
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view->format = dict->format ? dict->format : "B";
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view->ndim = dict->ndim;
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view->shape = dict->shape;
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view->itemsize = self->b_size;
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if (view->itemsize) {
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for (i = 0; i < view->ndim; ++i) {
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view->itemsize /= dict->shape[i];
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}
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}
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view->itemsize = item_dict->size;
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view->strides = NULL;
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view->suboffsets = NULL;
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view->internal = NULL;

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