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gh-91484: Allow memoryview cast for F-contiguous #137803

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gh-91484: Allow memoryview cast for F-contiguous #137803

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597ae6a
allow memoryview cast for F-contiguous
jamie2779 Aug 15, 2025
3cc8a7e
📜🤖 Added by blurb_it.
blurb-it[bot] Aug 15, 2025
20df3ab
fix lint issue
jamie2779 Aug 15, 2025
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26 changes: 26 additions & 0 deletions Lib/test/test_buffer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2846,6 +2846,32 @@ class BEPoint(ctypes.BigEndianStructure):
self.assertEqual(m2.strides, (1,))
self.assertEqual(m2.suboffsets, ())

def test_memoryview_cast_f_contiguous_ND_1D(self):
nd = ndarray(list(range(12)),shape=[3, 4], format='B', flags=ND_FORTRAN)
m = memoryview(nd)
self.assertTrue(m.f_contiguous)
self.assertTrue(m.contiguous)

m1 = m.cast('B')
self.assertEqual(m1.ndim, 1)
self.assertEqual(m1.shape, (m.nbytes,))
self.assertEqual(m1.strides, (1,))
self.assertTrue(m1.c_contiguous)
self.assertTrue(m1.contiguous)
self.assertEqual(m1.tobytes(), memoryview(nd).tobytes(order='F'))

for fmt in ('B', 'b', 'c', 'H', 'I'):
size = struct.calcsize(fmt)
if m.nbytes % size == 0:
m2 = m.cast(fmt)
self.assertEqual(m2.ndim, 1)
self.assertEqual(m2.shape, (m.nbytes // size,))
self.assertTrue(m2.contiguous)

m3 = m[::-1]
with self.assertRaises(TypeError):
m3.cast('B')

def test_memoryview_tolist(self):

# Most tolist() tests are in self.verify() etc.
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-08-15-06-28-45.gh-issue-91484.huCgHt.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
memoryview.cast() now allows casting from N-D to 1-D for F-contiguous.
8 changes: 5 additions & 3 deletions Objects/memoryobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1456,9 +1456,11 @@ memoryview_cast_impl(PyMemoryViewObject *self, PyObject *format,
CHECK_RESTRICTED(self);

if (!MV_C_CONTIGUOUS(self->flags)) {
PyErr_SetString(PyExc_TypeError,
"memoryview: casts are restricted to C-contiguous views");
return NULL;
if(shape || self->view.ndim == 1 || !MV_F_CONTIGUOUS(self->flags)) {
PyErr_SetString(PyExc_TypeError,
"memoryview: casts are restricted to C-contiguous views");
return NULL;
}
}
if ((shape || self->view.ndim != 1) && zero_in_shape(self)) {
PyErr_SetString(PyExc_TypeError,
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