Merge pull request #6747 from charris/deprecate-fortran-view

DEP: Deprecate changing shape of non-C-contiguous array via descr.

3 files changed, 47 insertions, 4 deletions

diff --git a/doc/release/1.11.0-notes.rst b/doc/release/1.11.0-notes.rst
index e60062c81..fac868ca3 100644
--- a/doc/release/1.11.0-notes.rst
+++ b/doc/release/1.11.0-notes.rst
@@ -18,6 +18,8 @@ Dropped Support
 Future Changes
 ==============
 
+* Relaxed stride checking will become the default.
+
 
 Compatibility notes
 ===================
@@ -103,3 +105,16 @@ Changes
 Deprecations
 ============
 
+Views of arrays in Fortran order
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The f_contiguous flag was used to signal that views as a dtypes that
+changed the element size would change the first index. This was always a
+bit problematical for arrays that were both f_contiguous and c_contiguous
+because c_contiguous took precendence. Relaxed stride checking results in
+more such dual contiguous arrays and breaks some existing code as a result.
+Note that this also affects changing the dtype by assigning to the dtype
+attribute of an array. The aim of this deprecation is to restrict views to
+c_contiguous arrays at some future time. A work around that is backward
+compatible is to use `a.T.view(...).T` instead. A parameter will also be
+added to the view method to explicitly ask for Fortran order views, but
+that will not be backward compatible.
diff --git a/numpy/core/src/multiarray/getset.c b/numpy/core/src/multiarray/getset.c
index 549ea333a..c2a88e3b9 100644
--- a/numpy/core/src/multiarray/getset.c
+++ b/numpy/core/src/multiarray/getset.c
@@ -488,11 +488,25 @@ array_descr_set(PyArrayObject *self, PyObject *arg)
 
 
     if ((newtype->elsize != PyArray_DESCR(self)->elsize) &&
-        (PyArray_NDIM(self) == 0 || !PyArray_ISONESEGMENT(self) ||
-         PyDataType_HASSUBARRAY(newtype))) {
+            (PyArray_NDIM(self) == 0 ||
+             !PyArray_ISONESEGMENT(self) ||
+             PyDataType_HASSUBARRAY(newtype))) {
         goto fail;
     }
-    if (PyArray_ISCONTIGUOUS(self)) {
+
+    /* Deprecate not C contiguous and a dimension changes */
+    if (newtype->elsize != PyArray_DESCR(self)->elsize &&
+            !PyArray_IS_C_CONTIGUOUS(self)) {
+        /* 11/27/2015 1.11.0 */
+        if (DEPRECATE("Changing the shape of non-C contiguous array by\n"
+                      "descriptor assignment is deprecated. To maintain\n"
+                      "the Fortran contiguity of a multidimensional Fortran\n"
+                      "array, use 'a.T.view(...).T' instead") < 0) {
+            return -1;
+        }
+    }
+
+    if (PyArray_IS_C_CONTIGUOUS(self)) {
         i = PyArray_NDIM(self) - 1;
     }
     else {
diff --git a/numpy/core/tests/test_deprecations.py b/numpy/core/tests/test_deprecations.py
index e2542195f..8f7e55d91 100644
--- a/numpy/core/tests/test_deprecations.py
+++ b/numpy/core/tests/test_deprecations.py
@@ -375,7 +375,7 @@ class TestBooleanIndexShapeMismatchDeprecation():
              arr.__getitem__, (slice(None), index))
 
 
-class TestFullDefaultDtype:
+class TestFullDefaultDtype(object):
     """np.full defaults to float when dtype is not set.  In the future, it will
     use the fill value's dtype.
     """
@@ -386,5 +386,19 @@ class TestFullDefaultDtype:
         assert_no_warnings(np.full, 1, 1, float)
 
 
+class TestNonCContiguousViewDeprecation(_DeprecationTestCase):
+    """View of non-C-contiguous arrays deprecated in 1.11.0.
+
+    The deprecation will not be raised for arrays that are both C and F
+    contiguous, as C contiguous is dominant. There are more such arrays
+    with relaxed stride checking than without so the deprecation is not
+    as visible with relaxed stride checking in force.
+    """
+
+    def test_fortran_contiguous(self):
+        self.assert_deprecated(np.ones((2,2)).T.view, args=(np.complex,))
+        self.assert_deprecated(np.ones((2,2)).T.view, args=(np.int8,))
+
+
 if __name__ == "__main__":
     run_module_suite()