Fix strides when creating Python buffer

2 files changed, 42 insertions, 0 deletions

diff --git a/numpy/core/src/multiarray/buffer.c b/numpy/core/src/multiarray/buffer.c
index ea1a885ed..e410f12b2 100644
--- a/numpy/core/src/multiarray/buffer.c
+++ b/numpy/core/src/multiarray/buffer.c
@@ -628,6 +628,8 @@ array_getbuffer(PyObject *obj, Py_buffer *view, int flags)
 {
     PyArrayObject *self;
     _buffer_info_t *info = NULL;
+    int i;
+    Py_ssize_t sd;
 
     self = (PyArrayObject*)obj;
 
@@ -702,6 +704,30 @@ array_getbuffer(PyObject *obj, Py_buffer *view, int flags)
     }
     if ((flags & PyBUF_STRIDES) == PyBUF_STRIDES) {
         view->strides = info->strides;
+
+#ifdef NPY_RELAXED_STRIDES_CHECKING
+        /*
+         * If NPY_RELAXED_STRIDES_CHECKING is on, the array may be
+         * contiguous, but it won't look that way to Python when it
+         * tries to determine contiguity by looking at the strides
+         * (since one of the elements may be -1).  In that case, just
+         * regenerate strides from shape.
+         */
+        if (PyArray_CHKFLAGS(self, NPY_ARRAY_C_CONTIGUOUS)) {
+            sd = view->itemsize;
+            for (i = view->ndim-1; i >= 0; --i) {
+                view->strides[i] = sd;
+                sd *= view->shape[i];
+            }
+        }
+        else if (PyArray_CHKFLAGS(self, NPY_ARRAY_F_CONTIGUOUS)) {
+            sd = view->itemsize;
+            for (i = 0; i < view->ndim; ++i) {
+                view->strides[i] = sd;
+                sd *= view->shape[i];
+            }
+        }
+#endif
     }
     else {
         view->strides = NULL;
diff --git a/numpy/core/tests/test_multiarray.py b/numpy/core/tests/test_multiarray.py
index 27f908fe4..a9b2d751f 100644
--- a/numpy/core/tests/test_multiarray.py
+++ b/numpy/core/tests/test_multiarray.py
@@ -4258,6 +4258,22 @@ class TestNewBufferProtocol(object):
         x3 = np.arange(dt3.itemsize, dtype=np.int8).view(dt3)
         self._check_roundtrip(x3)
 
+    def test_relaxed_strides(self):
+        # Test that relaxed strides are converted to non-relaxed
+        x = np.zeros((5, 10), dtype=">f4")
+
+        # Add an extra dimension in such a way that the strides will
+        # contain -1 markers
+        c = np.array([x])
+        assert memoryview(c).strides == (200, 40, 4)
+
+        # Writing C-contiguous data to a BytesIO buffer should work
+        fd = io.BytesIO()
+        fd.write(c.data)
+
+        fortran = c.T
+        assert memoryview(fortran).strides == (4, 40, 200)
+
 
 class TestArrayAttributeDeletion(object):