[Python-checkins] [3.10] gh-76963: PEP3118 itemsize of an empty ctypes array should not be 0 (GH-5576) (#100451)

Fri Dec 23 03:56:01 EST 2022

https://github.com/python/cpython/commit/95c55a69b3935e36108059ea89efd372d0902c6e
commit: 95c55a69b3935e36108059ea89efd372d0902c6e
branch: 3.10
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: mdickinson <dickinsm at gmail.com>
date: 2022年12月23日T08:55:55Z
summary:
[3.10] gh-76963: PEP3118 itemsize of an empty ctypes array should not be 0 (GH-5576) (#100451)
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.
(cherry picked from commit 84bc6a4f25fcf467813ee12b74118f7b1b54e285)
Co-authored-by: Eric Wieser <wieser.eric at gmail.com>
files:
A Misc/NEWS.d/next/Core and Builtins/2018-02-06-23-21-13.bpo-32782.EJVSfR.rst
M Lib/ctypes/test/test_pep3118.py
M Modules/_ctypes/_ctypes.c

diff --git a/Lib/ctypes/test/test_pep3118.py b/Lib/ctypes/test/test_pep3118.py
index 81e8ca7638fd..efffc80a66fc 100644
--- a/Lib/ctypes/test/test_pep3118.py
+++ b/Lib/ctypes/test/test_pep3118.py
@@ -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)),
diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-02-06-23-21-13.bpo-32782.EJVSfR.rst b/Misc/NEWS.d/next/Core and Builtins/2018-02-06-23-21-13.bpo-32782.EJVSfR.rst
new file mode 100644
index 000000000000..841740130bd1
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-02-06-23-21-13.bpo-32782.EJVSfR.rst	
@@ -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.
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 84378c40357b..a534a828d1ee 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -2795,11 +2795,33 @@ 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;
 
@@ -2812,12 +2834,7 @@ 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;
