python
@@ -873,3 +873,7 @@ Removed
 * Remove the ``PyUnicode_InternImmortal()`` function and the
   ``SSTATE_INTERNED_IMMORTAL`` macro.
   (Contributed by Victor Stinner in :gh:`85858`.)
+
+* Remove ``_use_broken_old_ctypes_structure_semantics_`` flag
+  from :mod:`ctypes` module.
+  (Contributed by Nikita Sobolev in :gh:`99285`.)
diff --git a/Include/internal/pycore_global_objects_fini_generated.h b/Include/internal/pycore_global_objects_fini_generated.h
diff --git a/Include/internal/pycore_global_strings.h b/Include/internal/pycore_global_strings.h
@@ -251,7 +251,6 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(_swappedbytes_)
         STRUCT_FOR_ID(_type_)
         STRUCT_FOR_ID(_uninitialized_submodules)
-        STRUCT_FOR_ID(_use_broken_old_ctypes_structure_semantics_)
         STRUCT_FOR_ID(_warn_unawaited_coroutine)
         STRUCT_FOR_ID(_xoptions)
         STRUCT_FOR_ID(a)

diff --git a/Include/internal/pycore_runtime_init_generated.h b/Include/internal/pycore_runtime_init_generated.h
diff --git a/Include/internal/pycore_unicodeobject_generated.h b/Include/internal/pycore_unicodeobject_generated.h
diff --git a/Misc/NEWS.d/next/Library/2022-11-09-12-36-12.gh-issue-99284.9p4J2l.rst b/Misc/NEWS.d/next/Library/2022-11-09-12-36-12.gh-issue-99284.9p4J2l.rst
@@ -0,0 +1,2 @@
+Remove ``_use_broken_old_ctypes_structure_semantics_``
+old untested and undocumented hack from :mod:`ctypes`.
diff --git a/Modules/_ctypes/stgdict.c b/Modules/_ctypes/stgdict.c
@@ -356,14 +356,6 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
     int big_endian;
     int arrays_seen = 0;
 
-    /* HACK Alert: I cannot be bothered to fix ctypes.com, so there has to
-       be a way to use the old, broken semantics: _fields_ are not extended
-       but replaced in subclasses.
-
-       XXX Remove this in ctypes 1.0!
-    */
-    int use_broken_old_ctypes_semantics;
-
     if (fields == NULL)
         return 0;
 
@@ -378,19 +370,6 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
         big_endian = PY_BIG_ENDIAN;
     }
 
-    if (_PyObject_LookupAttr(type,
-                &_Py_ID(_use_broken_old_ctypes_structure_semantics_), &tmp) < 0)
-    {
-        return -1;
-    }
-    if (tmp) {
-        Py_DECREF(tmp);
-        use_broken_old_ctypes_semantics = 1;
-    }
-    else {
-        use_broken_old_ctypes_semantics = 0;
-    }
-
     if (_PyObject_LookupAttr(type, &_Py_ID(_pack_), &tmp) < 0) {
         return -1;
     }
@@ -454,7 +433,7 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
     if (!isStruct) {
         stgdict->flags |= TYPEFLAG_HASUNION;
     }
-    if (basedict && !use_broken_old_ctypes_semantics) {
+    if (basedict) {
         size = offset = basedict->size;
         align = basedict->align;
         union_size = 0;
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Remove ``_use_broken_old_ctypes_structure_semantics_``
		old untested and undocumented hack from :mod:`ctypes`.