BUG: use correct input dtype in flatiter assignment

ngoldbaum · charris · commit 3d66056fa31a · 2025-09-05T13:43:25.000-06:00
diff --git a/numpy/_core/src/multiarray/iterators.c b/numpy/_core/src/multiarray/iterators.c
@@ -956,7 +956,7 @@ iter_ass_subscript(PyArrayIterObject *self, PyObject *ind, PyObject *val)
     /* We can assume the newly allocated array is aligned */
     int is_aligned = IsUintAligned(self->ao);
     if (PyArray_GetDTypeTransferFunction(
-                is_aligned, itemsize, itemsize, type, type, 0,
+                is_aligned, itemsize, itemsize, PyArray_DESCR(arrval), type, 0,
                 &cast_info, &transfer_flags) < 0) {
         goto finish;
     }
diff --git a/numpy/_core/tests/test_stringdtype.py b/numpy/_core/tests/test_stringdtype.py
@@ -531,6 +531,13 @@ def test_fancy_indexing(string_list):
         assert_array_equal(sarr[ind], uarr[ind])
 
 
+def test_flatiter_indexing():
+    # see gh-29659
+    arr = np.array(['hello', 'world'], dtype='T')
+    arr.flat[:] = 9223372036854775
+    assert_array_equal(arr, np.array([9223372036854775] * 2, dtype='T'))
+
+
 def test_creation_functions():
     assert_array_equal(np.zeros(3, dtype="T"), ["", "", ""])
     assert_array_equal(np.empty(3, dtype="T"), ["", "", ""])

Original file line number	Diff line number	Diff line change
`@@ -956,7 +956,7 @@ iter_ass_subscript(PyArrayIterObject self, PyObject ind, PyObject *val)`
`956`	`956`	`/* We can assume the newly allocated array is aligned */`
`957`	`957`	`int is_aligned = IsUintAligned(self->ao);`
`958`	`958`	`if (PyArray_GetDTypeTransferFunction(`
`959`		`- is_aligned, itemsize, itemsize, type, type, 0,`
	`959`	`+ is_aligned, itemsize, itemsize, PyArray_DESCR(arrval), type, 0,`
`960`	`960`	`&cast_info, &transfer_flags) < 0) {`
`961`	`961`	`goto finish;`
`962`	`962`	`}`