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gh-83791: Raise TypeError for len(memoryview_0d) (#18463)
Changes the behaviour of `len` on a zero-dimensional `memoryview` to raise `TypeError`. Previously, `len` would return `1`.
1 parent caed494 commit 3d2a468

5 files changed

Lines changed: 31 additions & 22 deletions

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‎Doc/library/stdtypes.rst‎

Lines changed: 9 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -3715,12 +3715,15 @@ copying.
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types such as :class:`bytes` and :class:`bytearray`, an element is a single
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byte, but other types such as :class:`array.array` may have bigger elements.
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3718-
``len(view)`` is equal to the length of :class:`~memoryview.tolist`.
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If ``view.ndim = 0``, the length is 1. If ``view.ndim = 1``, the length
3720-
is equal to the number of elements in the view. For higher dimensions,
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the length is equal to the length of the nested list representation of
3722-
the view. The :class:`~memoryview.itemsize` attribute will give you the
3723-
number of bytes in a single element.
3718+
``len(view)`` is equal to the length of :class:`~memoryview.tolist`, which
3719+
is the nested list representation of the view. If ``view.ndim = 1``,
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this is equal to the number of elements in the view.
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.. versionchanged:: 3.12
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If ``view.ndim == 0``, ``len(view)`` now raises :exc:`TypeError` instead of returning 1.
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The :class:`~memoryview.itemsize` attribute will give you the number of
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bytes in a single element.
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A :class:`memoryview` supports slicing and indexing to expose its data.
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One-dimensional slicing will result in a subview::

‎Lib/test/test_buffer.py‎

Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -965,8 +965,10 @@ def check_memoryview(m, expected_readonly=readonly):
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self.assertEqual(m.strides, tuple(strides))
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self.assertEqual(m.suboffsets, tuple(suboffsets))
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968-
n = 1 if ndim == 0 else len(lst)
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self.assertEqual(len(m), n)
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if ndim == 0:
969+
self.assertRaises(TypeError, len, m)
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else:
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self.assertEqual(len(m), len(lst))
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rep = result.tolist() if fmt else result.tobytes()
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self.assertEqual(rep, lst)

‎Lib/test/test_ctypes/test_pep3118.py‎

Lines changed: 11 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -28,7 +28,7 @@ def test_native_types(self):
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if shape:
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self.assertEqual(len(v), shape[0])
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else:
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self.assertEqual(len(v) * sizeof(itemtp), sizeof(ob))
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self.assertRaises(TypeError, len, v)
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self.assertEqual(v.itemsize, sizeof(itemtp))
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self.assertEqual(v.shape, shape)
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# XXX Issue #12851: PyCData_NewGetBuffer() must provide strides
@@ -39,11 +39,10 @@ def test_native_types(self):
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# they are always read/write
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self.assertFalse(v.readonly)
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42-
if v.shape:
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n = 1
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for dim in v.shape:
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n = n * dim
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self.assertEqual(n * v.itemsize, len(v.tobytes()))
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n = 1
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for dim in v.shape:
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n = n * dim
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self.assertEqual(n * v.itemsize, len(v.tobytes()))
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except:
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# so that we can see the failing type
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print(tp)
@@ -58,7 +57,7 @@ def test_endian_types(self):
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if shape:
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self.assertEqual(len(v), shape[0])
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else:
61-
self.assertEqual(len(v) * sizeof(itemtp), sizeof(ob))
60+
self.assertRaises(TypeError, len, v)
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self.assertEqual(v.itemsize, sizeof(itemtp))
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self.assertEqual(v.shape, shape)
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# XXX Issue #12851
@@ -67,11 +66,10 @@ def test_endian_types(self):
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# they are always read/write
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self.assertFalse(v.readonly)
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70-
if v.shape:
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n = 1
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for dim in v.shape:
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n = n * dim
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self.assertEqual(n, len(v))
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n = 1
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for dim in v.shape:
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n = n * dim
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self.assertEqual(n * v.itemsize, len(v.tobytes()))
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except:
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# so that we can see the failing type
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print(tp)
@@ -243,7 +241,7 @@ class LEPoint(LittleEndianStructure):
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#
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endian_types = [
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(BEPoint, "T{>l:x:>l:y:}".replace('l', s_long), (), BEPoint),
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(LEPoint, "T{<l:x:<l:y:}".replace('l', s_long), (), LEPoint),
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(LEPoint * 1, "T{<l:x:<l:y:}".replace('l', s_long), (1,), LEPoint),
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(POINTER(BEPoint), "&T{>l:x:>l:y:}".replace('l', s_long), (), POINTER(BEPoint)),
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(POINTER(LEPoint), "&T{<l:x:<l:y:}".replace('l', s_long), (), POINTER(LEPoint)),
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]

‎Misc/NEWS.d/next/Core and Builtins/2020-02-11-15-54-40.bpo-39610.fvgsCl.rst‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
``len()`` for 0-dimensional :class:`memoryview`` objects (such as ``memoryview(ctypes.c_uint8(42))``) now raises a :exc:`TypeError`.
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Previously this returned ``1``, which was not consistent with ``mem_0d[0]`` raising an :exc:`IndexError``.

‎Objects/memoryobject.c‎

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2642,7 +2642,11 @@ static Py_ssize_t
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memory_length(PyMemoryViewObject *self)
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{
26442644
CHECK_RELEASED_INT(self);
2645-
return self->view.ndim == 0 ? 1 : self->view.shape[0];
2645+
if (self->view.ndim == 0) {
2646+
PyErr_SetString(PyExc_TypeError, "0-dim memory has no length");
2647+
return -1;
2648+
}
2649+
return self->view.shape[0];
26462650
}
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/* As mapping */

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