numpy · seberg · Jun 20, 2025 · May 8, 2025 · May 8, 2025 · May 8, 2025
diff --git a/doc/release/upcoming_changes/28925.deprecation.rst b/doc/release/upcoming_changes/28925.deprecation.rst
@@ -0,0 +1,9 @@
+Setting the ``strides`` attribute is deprecated
+-----------------------------------------------
+Setting the strides attribute is now deprecated since mutating
+an array is unsafe if an array is shared, especially by multiple
+threads.  As an alternative, you can create a new view (no copy) via:
+* `np.lib.stride_tricks.strided_window_view` if applicable,
+* `np.lib.stride_tricks.as_strided` for the general case,
+* or the `np.ndarray` constructor (``buffer`` is the original array) for a light-weight version.
+
diff --git a/numpy/__init__.pyi b/numpy/__init__.pyi
@@ -217,7 +217,7 @@ from typing import (
 # library include `typing_extensions` stubs:
 # https://github.com/python/typeshed/blob/main/stdlib/typing_extensions.pyi
 from _typeshed import Incomplete, StrOrBytesPath, SupportsFlush, SupportsLenAndGetItem, SupportsWrite
-from typing_extensions import CapsuleType, TypeVar
+from typing_extensions import CapsuleType, TypeVar, deprecated
 
 from numpy import (
     char,
@@ -2169,6 +2169,7 @@ class ndarray(_ArrayOrScalarCommon, Generic[_ShapeT_co, _DTypeT_co]):
     def shape(self, value: _ShapeLike) -> None: ...
     @property
     def strides(self) -> _Shape: ...
+    @deprecated("Setting the strides on a NumPy array has been deprecated in NumPy 2.4")
     @strides.setter
     def strides(self, value: _ShapeLike) -> None: ...
     def byteswap(self, inplace: builtins.bool = ...) -> Self: ...

diff --git a/numpy/_core/src/multiarray/getset.c b/numpy/_core/src/multiarray/getset.c
@@ -85,7 +85,7 @@ array_shape_set(PyArrayObject *self, PyObject *val, void* NPY_UNUSED(ignored))
         /* Free old dimensions and strides */
         npy_free_cache_dim_array(self);
         ((PyArrayObject_fields *)self)->nd = nd;
-        ((PyArrayObject_fields *)self)->dimensions = _dimensions; 
+        ((PyArrayObject_fields *)self)->dimensions = _dimensions;
         ((PyArrayObject_fields *)self)->strides = _dimensions + nd;
 
         if (nd) {
@@ -95,7 +95,7 @@ array_shape_set(PyArrayObject *self, PyObject *val, void* NPY_UNUSED(ignored))
     }
     else {
         /* Free old dimensions and strides */
-        npy_free_cache_dim_array(self);        
+        npy_free_cache_dim_array(self);
         ((PyArrayObject_fields *)self)->nd = 0;
         ((PyArrayObject_fields *)self)->dimensions = NULL;
         ((PyArrayObject_fields *)self)->strides = NULL;
@@ -116,6 +116,19 @@ array_strides_get(PyArrayObject *self, void *NPY_UNUSED(ignored))
 static int
 array_strides_set(PyArrayObject *self, PyObject *obj, void *NPY_UNUSED(ignored))
 {
+    if (obj == NULL) {
+        PyErr_SetString(PyExc_AttributeError,
+                "Cannot delete array strides");
+        return -1;
+    }
+
+    /* Deprecated NumPy 2.4, 2025-05-11 */
+    if (DEPRECATE("Setting the strides on a NumPy array has been deprecated in NumPy 2.4.\n"
+                  "As an alternative, you can create a new view using np.lib.stride_tricks.as_strided."
+                 ) < 0 ) {
+        return -1;
+    }
+
     PyArray_Dims newstrides = {NULL, -1};
     PyArrayObject *new;
     npy_intp numbytes = 0;
@@ -124,11 +137,6 @@ array_strides_set(PyArrayObject *self, PyObject *obj, void *NPY_UNUSED(ignored))
     npy_intp upper_offset = 0;
     Py_buffer view;
 
-    if (obj == NULL) {
-        PyErr_SetString(PyExc_AttributeError,
-                "Cannot delete array strides");
-        return -1;
-    }
     if (!PyArray_OptionalIntpConverter(obj, &newstrides) ||
         newstrides.len == -1) {
         PyErr_SetString(PyExc_TypeError, "invalid strides");

diff --git a/numpy/_core/tests/test_api.py b/numpy/_core/tests/test_api.py
@@ -5,6 +5,7 @@
 import numpy as np
 import numpy._core.umath as ncu
 from numpy._core._rational_tests import rational
+from numpy.lib import stride_tricks
 from numpy.testing import (
     HAS_REFCOUNT,
     assert_,
@@ -558,7 +559,7 @@ def check_copy_result(x, y, ccontig, fcontig, strides=False):
 
 def test_contiguous_flags():
     a = np.ones((4, 4, 1))[::2, :, :]
-    a.strides = a.strides[:2] + (-123,)
+    a = stride_tricks.as_strided(a, strides=a.strides[:2] + (-123,))
     b = np.ones((2, 2, 1, 2, 2)).swapaxes(3, 4)
 
     def check_contig(a, ccontig, fcontig):

diff --git a/numpy/_core/tests/test_deprecations.py b/numpy/_core/tests/test_deprecations.py
@@ -406,6 +406,13 @@ def __array_wrap__(self, arr):
         self.assert_deprecated(lambda: np.negative(test2))
         assert test2.called
 
+class TestDeprecatedArrayAttributeSetting(_DeprecationTestCase):
+    message = "Setting the .*on a NumPy array has been deprecated.*"
+
+    def test_deprecated_strides_set(self):
+        x = np.eye(2)
+        self.assert_deprecated(setattr, args=(x, 'strides', x.strides))
+
 
 class TestDeprecatedDTypeParenthesizedRepeatCount(_DeprecationTestCase):
     message = "Passing in a parenthesized single number"

diff --git a/numpy/_core/tests/test_half.py b/numpy/_core/tests/test_half.py
@@ -21,7 +21,7 @@ class TestHalf:
     def setup_method(self):
         # An array of all possible float16 values
         self.all_f16 = np.arange(0x10000, dtype=uint16)
-        self.all_f16.dtype = float16
+        self.all_f16 = self.all_f16.view(float16)
 
         # NaN value can cause an invalid FP exception if HW is being used
         with np.errstate(invalid='ignore'):
@@ -32,7 +32,7 @@ def setup_method(self):
         self.nonan_f16 = np.concatenate(
                                 (np.arange(0xfc00, 0x7fff, -1, dtype=uint16),
                                  np.arange(0x0000, 0x7c01, 1, dtype=uint16)))
-        self.nonan_f16.dtype = float16
+        self.nonan_f16 = self.nonan_f16.view(float16)
         self.nonan_f32 = np.array(self.nonan_f16, dtype=float32)
         self.nonan_f64 = np.array(self.nonan_f16, dtype=float64)
 
@@ -218,7 +218,7 @@ def test_half_values(self):
                       0x0001, 0x8001,
                       0x0000, 0x8000,
                       0x7c00, 0xfc00], dtype=uint16)
-        b.dtype = float16
+        b = b.view(dtype=float16)
         assert_equal(a, b)
 
     def test_half_rounding(self):

diff --git a/numpy/_core/tests/test_multiarray.py b/numpy/_core/tests/test_multiarray.py
@@ -29,6 +29,7 @@
 from numpy._core.multiarray import _get_ndarray_c_version, dot
 from numpy._core.tests._locales import CommaDecimalPointLocale
 from numpy.exceptions import AxisError, ComplexWarning
+from numpy.lib import stride_tricks
 from numpy.lib.recfunctions import repack_fields
 from numpy.testing import (
     BLAS_SUPPORTS_FPE,
@@ -382,7 +383,8 @@ def make_array(size, offset, strides):
                                offset=offset * x.itemsize)
             except Exception as e:
8000
                 raise RuntimeError(e)
-            r.strides = strides = strides * x.itemsize
+            with pytest.warns(DeprecationWarning):
+                r.strides = strides * x.itemsize
             return r
 
         assert_equal(make_array(4, 4, -1), np.array([4, 3, 2, 1]))
@@ -392,24 +394,28 @@ def make_array(size, offset, strides):
         assert_raises(RuntimeError, make_array, 8, 3, 1)
         # Check that the true extent of the array is used.
         # Test relies on as_strided base not exposing a buffer.
-        x = np.lib.stride_tricks.as_strided(np.arange(1), (10, 10), (0, 0))
+        x = stride_tricks.as_strided(np.arange(1), (10, 10), (0, 0))
 
         def set_strides(arr, strides):
-            arr.strides = strides
+            with pytest.warns(DeprecationWarning):
+                arr.strides = strides
 
         assert_raises(ValueError, set_strides, x, (10 * x.itemsize, x.itemsize))
 
         # Test for offset calculations:
-        x = np.lib.stride_tricks.as_strided(np.arange(10, dtype=np.int8)[-1],
+        x = stride_tricks.as_strided(np.arange(10, dtype=np.int8)[-1],
                                                     shape=(10,), strides=(-1,))
         assert_raises(ValueError, set_strides, x[::-1], -1)
         a = x[::-1]
-        a.strides = 1
-        a[::2].strides = 2
+        with pytest.warns(DeprecationWarning):
+            a.strides = 1
+        with pytest.warns(DeprecationWarning):
+            a[::2].strides = 2
 
         # test 0d
         arr_0d = np.array(0)
-        arr_0d.strides = ()
+        with pytest.warns(DeprecationWarning):
+            arr_0d.strides = ()
         assert_raises(TypeError, set_strides, arr_0d, None)
 
     def test_fill(self):
@@ -3635,7 +3641,7 @@ def test_ravel(self):
         a = a.reshape(2, 1, 2, 2).swapaxes(-1, -2)
        strides = list(a.strides)
         strides[1] = 123
-        a.strides = strides
+        a = stride_tricks.as_strided(a, strides=strides)
         assert_(a.ravel(order='K').flags.owndata)
         assert_equal(a.ravel('K'), np.arange(0, 15, 2))
 
@@ -3644,7 +3650,7 @@ def test_ravel(self):
         a = a.reshape(2, 1, 2, 2).swapaxes(-1, -2)
         strides = list(a.strides)
         strides[1] = 123
-        a.strides = strides
+        a = stride_tricks.as_strided(a, strides=strides)
         assert_(np.may_share_memory(a.ravel(order='K'), a))
         assert_equal(a.ravel(order='K'), np.arange(2**3))
 
@@ -3657,7 +3663,7 @@ def test_ravel(self):
 
         # 1-element tidy strides test:
         a = np.array([[1]])
-        a.strides = (123, 432)
+        a = stride_tricks.as_strided(a, strides=(123, 432))
         if np.ones(1).strides == (8,):
             assert_(np.may_share_memory(a.ravel('K'), a))
             assert_equal(a.ravel('K').strides, (a.dtype.itemsize,))
@@ -4546,7 +4552,8 @@ def test_datetime64_byteorder(self):
         original = np.array([['2015-02-24T00:00:00.000000000']], dtype='datetime64[ns]')
 
         original_byte_reversed = original.copy(order='K')
-        original_byte_reversed.dtype = original_byte_reversed.dtype.newbyteorder('S')
+        new_dtype = original_byte_reversed.dtype.newbyteorder('S')
+        original_byte_reversed = original_byte_reversed.view(dtype=new_dtype)
         original_byte_reversed.byteswap(inplace=True)
 
         new = pickle.loads(pickle.dumps(original_byte_reversed))
@@ -8366,10 +8373,13 @@ def test_padded_struct_array(self):
            self._check_roundtrip(x3)
 
     @pytest.mark.valgrind_error(reason="leaks buffer info cache temporarily.")
-    def test_relaxed_strides(self, c=np.ones((1, 10, 10), dtype='i8')):  # noqa: B008
+    def test_relaxed_strides(self, c=stride_tricks.as_strided(  # noqa: B008
+                                              np.ones((1, 10, 10), dtype='i8'),  # noqa: B008
+                                              strides=(-1, 80, 8)
+                                              )
+                                  ):
         # Note: c defined as parameter so that it is persistent and leak
         # checks will notice gh-16934 (buffer info cache leak).
-        c.strides = (-1, 80, 8)  # strides need to be fixed at export
 
         assert_(memoryview(c).strides == (800, 80, 8))
 

diff --git a/numpy/_core/tests/test_nditer.py b/numpy/_core/tests/test_nditer.py
@@ -858,7 +858,7 @@ def test_iter_nbo_align_contig():
 
     # Unaligned input
     a = np.zeros((6 * 4 + 1,), dtype='i1')[1:]
-    a.dtype = 'f4'
+    a = a.view('f4')
     a[:] = np.arange(6, dtype='f4')
     assert_(not a.flags.aligned)
     # Without 'aligned', shouldn't copy
@@ -1803,7 +1803,7 @@ def test_iter_buffering():
     arrays.append(np.arange(10, dtype='f4'))
     # Unaligned array
     a = np.zeros((4 * 16 + 1,), dtype='i1')[1:]
-    a.dtype = 'i4'
+    a = a.view('i4')
     a[:] = np.arange(16, dtype='i4')
     arrays.append(a)
     # 4-D F-order array

diff --git a/numpy/_core/tests/test_regression.py b/numpy/_core/tests/test_regression.py
@@ -12,6 +12,7 @@
 import numpy as np
 from numpy._utils import asbytes, asunicode
 from numpy.exceptions import AxisError, ComplexWarning
+from numpy.lib.stride_tricks import as_strided
 from numpy.testing import (
     HAS_REFCOUNT,
     IS_64BIT,
@@ -208,7 +209,7 @@ def test_mem_dot(self):
         # Dummy array to detect bad memory access:
         _z = np.ones(10)
         _dummy = np.empty((0, 10))
-        z = np.lib.stride_tricks.as_strided(_z, _dummy.shape, _dummy.strides)
+        z = as_strided(_z, _dummy.shape, _dummy.strides)
         np.dot(x, np.transpose(y), out=z)
         assert_equal(_z, np.ones(10))
         # Do the same for the built-in dot:
@@ -438,19 +439,16 @@ def test_lexsort_zerolen_custom_strides(self):
         xs = np.array([], dtype='i8')
         assert np.lexsort((xs,)).shape[0] == 0  # Works
 
-        xs.strides = (16,)
+        xs = as_strided(xs, strides=(16,))
         assert np.lexsort((xs,)).shape[0] == 0  # Was: MemoryError
 
     def test_lexsort_zerolen_custom_strides_2d(self):
         xs = np.array([], dtype='i8')
+        xt = as_strided(xs, shape=(0, 2), strides=(16, 16))
+        assert np.lexsort((xt,), axis=0).shape[0] == 0
 
-        xs.shape = (0, 2)
-        xs.strides = (16, 16)
-        assert np.lexsort((xs,), axis=0).shape[0] == 0
-
-        xs.shape = (2, 0)
-        xs.strides = (16, 16)
-        assert np.lexsort((xs,), axis=0).shape[0] == 2
+        xt = as_strided(xs, shape=(2, 0), strides=(16, 16))
+        assert np.lexsort((xt,), axis=0).shape[0] == 2
 
     def test_lexsort_invalid_axis(self):
         assert_raises(AxisError, np.lexsort, (np.arange(1),), axis=2)
@@ -644,7 +642,7 @@ def test_reshape_order(self):
     def test_reshape_zero_strides(self):
         # Issue #380, test reshaping of zero strided arrays
         a = np.ones(1)
-        a = np.lib.stride_tricks.as_strided(a, shape=(5,), strides=(0,))
+        a = as_strided(a, shape=(5,), strides=(0,))
         assert_(a.reshape(5, 1).strides[0] == 0)
 
     def test_reshape_zero_size(self):
@@ -1654,7 +1652,7 @@ def test_eq_string_and_object_array(self):
 
     def test_nonzero_byteswap(self):
         a = np.array([0x80000000, 0x00000080, 0], dtype=np.uint32)
-        a.dtype = np.float32
+        a = a.view(np.float32)
         assert_equal(a.nonzero()[0], [1])
         a = a.byteswap()
         a = a.view(a.dtype.newbyteorder())
@@ -1878,7 +1876,8 @@ def test_alignment_update(self):
         # Check that alignment flag is updated on stride setting
         a = np.arange(10)
         assert_(a.flags.aligned)
-        a.strides = 3
+        with pytest.warns(DeprecationWarning):
+            a.strides = 3
         assert_(not a.flags.aligned)
 
     def test_ticket_1770(self):

diff --git a/numpy/lib/_npyio_impl.py b/numpy/lib/_npyio_impl.py
@@ -1730,7 +1730,7 @@ def fromregex(file, regexp, dtype, encoding=None):
             #   re-interpret as a single-field structured array.
             newdtype = np.dtype(dtype[dtype.names[0]])
             output = np.array(seq, dtype=newdtype)
-            output.dtype = dtype
+            output = output.view(dtype)
         else:
             output = np.array(seq, dtype=dtype)