Consolidate all array writeability checking in new PyArray_RequireWriteable

This is mostly a code cleanup, but it does have a user-visible effect
in that attempting to write to a unwriteable array now consistently
raises ValueError. (It used to randomly raise either ValueError or
RuntimeError.)

Passes numpy.test("full").

1 files changed, 13 insertions, 0 deletions

diff --git a/doc/release/2.0.0-notes.rst b/doc/release/2.0.0-notes.rst
index 3b61afc31..978d9139e 100644
--- a/doc/release/2.0.0-notes.rst
+++ b/doc/release/2.0.0-notes.rst
@@ -148,6 +148,14 @@ New argument to searchsorted
 The function searchsorted now accepts a 'sorter' argument that is a
 permuation array that sorts the array to search.
 
+C API
+-----
+
+New function ``PyArray_RequireWriteable`` provides a consistent
+interface for checking array writeability -- any C code which works
+with arrays whose WRITEABLE flag is not know to be True a priori,
+should make sure to call this function before writing.
+
 Changes
 =======
 
@@ -166,6 +174,11 @@ during alpha or early beta testing, and a decision to either keep the
 stricter behavior, or add in a hack to allow the previous behavior to
 work.
 
+Attempting to write to a read-only array (one with
+``arr.flags.writeable`` set to ``False``) used to raise either a
+RuntimeError, ValueError, or TypeError inconsistently, depending on
+which code path was taken. It now consistently raises a ValueError.
+
 The functions np.diag, np.diagonal, and <ndarray>.diagonal now return a
 view into the original array instead of making a copy. This makes these
 functions more consistent with NumPy's general approach of taking views