Add What's New entry

encukou · encukou · commit 075ca515ef21 · 2023-04-17T14:27:12.000+02:00
diff --git a/Doc/whatsnew/3.12.rst b/Doc/whatsnew/3.12.rst
@@ -1014,6 +1014,21 @@ New Features
 
   (Contributed by Petr Viktorin in :gh:`101101`.)
 
+* :pep:`697`: Added API for extending types whose instance memory layout is
+  opaque:
+
+  - :c:member:`PyType_Spec.basicsize` can be zero or negative to specify
+    inheriting or extending the base class size.
+  - :c:func:`PyObject_GetTypeData` and :c:func:`PyType_GetTypeDataSize`
+    added to allow access to subclass-specific instance data.
+  - :c:macro:`Py_TPFLAGS_ITEMS_AT_END` and :c:func:`PyObject_GetItemData`
+    added to allow safely extending certain variable-sized types, including
+    :c:var:`PyType_Type`.
+  - :c:macro:`Py_RELATIVE_OFFSET` added to allow defining
+    :c:type:`members <PyMemberDef>` in terms of a subclass-specific struct.
+
+  (Contributed by Petr Viktorin in :gh:`103509`.)
+
 * Added the new limited C API function :c:func:`PyType_FromMetaclass`,
   which generalizes the existing :c:func:`PyType_FromModuleAndSpec` using
   an additional metaclass argument.
