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gh-83791: Raise TypeError for len(memoryview_0d) #18463

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Merged
mdickinson merged 8 commits into from
Apr 22, 2023
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gh-83791: Raise TypeError for len(memoryview_0d) #18463

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c210029
bpo-39610: Raise TypeError for len(memoryview_0d)
eric-wieser Feb 11, 2020
a352888
Update Doc/library/stdtypes.rst
eric-wieser Aug 29, 2020
209644d
Merge remote-tracking branch 'upstream/main' into fix-memorview-__len…
eric-wieser Jul 7, 2022
dbad24a
Fix documentation build
eric-wieser Jul 7, 2022
6efc1c6
Merge branch 'main' into fix-memorview-__len__-issue39610
eric-wieser Feb 21, 2023
d6b38b9
Bump version in `versionchanged`
eric-wieser Feb 21, 2023
4e24952
Sphinx formatting
eric-wieser Apr 12, 2023
31ca563
Merge branch 'main' into fix-memorview-__len__-issue39610
eric-wieser Apr 12, 2023
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15 changes: 9 additions & 6 deletions Doc/library/stdtypes.rst
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Expand Up @@ -3714,12 +3714,15 @@ copying.
types such as :class:`bytes` and :class:`bytearray`, an element is a single
byte, but other types such as :class:`array.array` may have bigger elements.

``len(view)`` is equal to the length of :class:`~memoryview.tolist`.
If ``view.ndim = 0``, the length is 1. If ``view.ndim = 1``, the length
is equal to the number of elements in the view. For higher dimensions,
the length is equal to the length of the nested list representation of
the view. The :class:`~memoryview.itemsize` attribute will give you the
number of bytes in a single element.
``len(view)`` is equal to the length of :class:`~memoryview.tolist`, which
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@serhiy-storchaka serhiy-storchaka Mar 14, 2020

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Since the documented behavior was changed, it needs a versionchanged directive and an entry in What's New.

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@eric-wieser eric-wieser May 30, 2020

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Should I put this in the 3.9 what's new? This sounds like a recipe for merge conflicts, until the rest of the patch has general approval.

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@eric-wieser eric-wieser Aug 28, 2020

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Just checking in on this - what's the procedure for adding a what's new entry if I have no idea which python version this will end up being merged into?

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@skrah skrah Aug 29, 2020

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You can use version 3.10. It cannot go into earlier versions since it's a behavior change. And we have ample time for deliberation on how the documented behavior emerged.

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@eric-wieser eric-wieser Jul 7, 2022

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I've update it to say 3.11, since it's been two years since I changed it to say 3.10. Let me know if it should be 3.12 instead.

is the nested list representation of the view. If ``view.ndim = 1``,
this is equal to the number of elements in the view.
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.. versionchanged:: 3.12
If ``view.ndim == 0``, ``len(view)`` now raises :exc:`TypeError` instead of returning 1.

The :class:`~memoryview.itemsize` attribute will give you the number of
bytes in a single element.

A :class:`memoryview` supports slicing and indexing to expose its data.
One-dimensional slicing will result in a subview::
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6 changes: 4 additions & 2 deletions Lib/test/test_buffer.py
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Expand Up @@ -965,8 +965,10 @@ def check_memoryview(m, expected_readonly=readonly):
self.assertEqual(m.strides, tuple(strides))
self.assertEqual(m.suboffsets, tuple(suboffsets))

n = 1 if ndim == 0 else len(lst)
self.assertEqual(len(m), n)
if ndim == 0:
self.assertRaises(TypeError, len, m)
else:
self.assertEqual(len(m), len(lst))

rep = result.tolist() if fmt else result.tobytes()
self.assertEqual(rep, lst)
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24 changes: 11 additions & 13 deletions Lib/test/test_ctypes/test_pep3118.py
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Expand Up @@ -28,7 +28,7 @@ def test_native_types(self):
if shape:
self.assertEqual(len(v), shape[0])
else:
self.assertEqual(len(v) * sizeof(itemtp), sizeof(ob))
self.assertRaises(TypeError, len, v)
self.assertEqual(v.itemsize, sizeof(itemtp))
self.assertEqual(v.shape, shape)
# XXX Issue #12851: PyCData_NewGetBuffer() must provide strides
Expand All @@ -39,11 +39,10 @@ def test_native_types(self):
# they are always read/write
self.assertFalse(v.readonly)

if v.shape:
n = 1
for dim in v.shape:
n = n * dim
self.assertEqual(n * v.itemsize, len(v.tobytes()))
n = 1
for dim in v.shape:
n = n * dim
self.assertEqual(n * v.itemsize, len(v.tobytes()))
except:
# so that we can see the failing type
print(tp)
Expand All @@ -58,7 +57,7 @@ def test_endian_types(self):
if shape:
self.assertEqual(len(v), shape[0])
else:
self.assertEqual(len(v) * sizeof(itemtp), sizeof(ob))
self.assertRaises(TypeError, len, v)
self.assertEqual(v.itemsize, sizeof(itemtp))
self.assertEqual(v.shape, shape)
# XXX Issue #12851
Expand All @@ -67,11 +66,10 @@ def test_endian_types(self):
# they are always read/write
self.assertFalse(v.readonly)

if v.shape:
n = 1
for dim in v.shape:
n = n * dim
self.assertEqual(n, len(v))
n = 1
for dim in v.shape:
n = n * dim
self.assertEqual(n * v.itemsize, len(v.tobytes()))
except:
# so that we can see the failing type
print(tp)
Expand Down Expand Up @@ -243,7 +241,7 @@ class LEPoint(LittleEndianStructure):
#
endian_types = [
(BEPoint, "T{>l:x:>l:y:}".replace('l', s_long), (), BEPoint),
(LEPoint, "T{<l:x:<l:y:}".replace('l', s_long), (), LEPoint),
(LEPoint * 1, "T{<l:x:<l:y:}".replace('l', s_long), (1,), LEPoint),
(POINTER(BEPoint), "&T{>l:x:>l:y:}".replace('l', s_long), (), POINTER(BEPoint)),
(POINTER(LEPoint), "&T{<l:x:<l:y:}".replace('l', s_long), (), POINTER(LEPoint)),
]
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-02-11-15-54-40.bpo-39610.fvgsCl.rst
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@@ -0,0 +1,2 @@
``len()`` for 0-dimensional :class:`memoryview`` objects (such as ``memoryview(ctypes.c_uint8(42))``) now raises a :exc:`TypeError`.
Previously this returned ``1``, which was not consistent with ``mem_0d[0]`` raising an :exc:`IndexError``.
6 changes: 5 additions & 1 deletion Objects/memoryobject.c
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Expand Up @@ -2642,7 +2642,11 @@ static Py_ssize_t
memory_length(PyMemoryViewObject *self)
{
CHECK_RELEASED_INT(self);
return self->view.ndim == 0 ? 1 : self->view.shape[0];
if (self->view.ndim == 0) {
PyErr_SetString(PyExc_TypeError, "0-dim memory has no length");
return -1;
}
return self->view.shape[0];
}

/* As mapping */
Expand Down