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Commit29b3c32

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bpo-32782: PEP3118 itemsize of an empty ctypes array should not be 0
The itemsize returned in a memoryview of a ctypes array should be computed from the item type, not by dividing the total size by the length and assuming that the length is not zero.
1 parentc1e46e9 commit29b3c32

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3 files changed

+44
-5
lines changed

3 files changed

+44
-5
lines changed

‎Lib/ctypes/test/test_pep3118.py

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -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)),
Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,3 @@
1+
``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

Lines changed: 39 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -2596,10 +2596,45 @@ static PyMemberDef PyCData_members[] = {
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{NULL },
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};
25982598

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/*
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Get the StgDictObject corresponding to a single item of a multidimensional
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array.
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Takes and returns a borrowed reference.
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*/
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staticStgDictObject*PyCData_item_stgdict(StgDictObject*dict)
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{
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if (dict->ndim==0) {
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/* scalar is its own item */
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returndict;
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}
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else {
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/* follow _type_, eliminating a dimension */
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PyObject*type_attr;
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StgDictObject*item_dict;
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type_attr=PyDict_GetItemString((PyObject*)dict,"_type_");
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if (!type_attr) {
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PyErr_SetString(PyExc_AttributeError,
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"class must define a '_type_' attribute");
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returnNULL;
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}
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2622+
item_dict=PyType_stgdict(type_attr);
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if (!item_dict) {
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PyErr_SetString(PyExc_TypeError,
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"_type_ must have storage info");
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returnNULL;
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}
2628+
2629+
returnPyCData_item_stgdict(item_dict);
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}
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}
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staticintPyCData_NewGetBuffer(PyObject*myself,Py_buffer*view,intflags)
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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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StgDictObject*item_dict;
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Py_ssize_ti;
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26052640
if (view==NULL)return0;
@@ -2613,12 +2648,11 @@ 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;
2616-
view->itemsize=self->b_size;
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if (view->itemsize) {
2618-
for (i=0;i<view->ndim;++i) {
2619-
view->itemsize /=dict->shape[i];
2620-
}
2651+
item_dict=PyCData_item_stgdict(dict);
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if (item_dict==NULL) {
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return-1;
26212654
}
2655+
view->itemsize=item_dict->size;
26222656
view->strides=NULL;
26232657
view->suboffsets=NULL;
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view->internal=NULL;

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