bpo-32388: Remove cross-version binary compatibility requirement in tp_flags (GH...

It is now allowed to add new fields at the end of the PyTypeObject struct without having to allocate a dedicated compatibility flag in tp_flags.

This will reduce the risk of running out of bits in the 32-bit tp_flags value.

diff --git a/Doc/c-api/typeobj.rst b/Doc/c-api/typeobj.rst
index aa667846a0da26b7e206a276425d3258b6dbca4c..e2f8f54be79ae89e342c3ee85c290b8996f2af04 100644 (file)
--- a/Doc/c-api/typeobj.rst
+++ b/Doc/c-api/typeobj.rst
@@ -1099,6 +1099,11 @@ and :c:type:`PyType_Type` effectively act as defaults.)
 
       .. versionadded:: 3.4
 
+      .. deprecated:: 3.8
+         This flag isn't necessary anymore, as the interpreter assumes the
+         :c:member:`~PyTypeObject.tp_finalize` slot is always present in the
+         type structure.
+
 
 .. c:member:: const char* PyTypeObject.tp_doc
 

diff --git a/Doc/whatsnew/3.8.rst b/Doc/whatsnew/3.8.rst
index b4a80309170152f28e3c18c5dc6c5704ed2ed969..5cd9a8edc7935d3ceb2948d5c8eb5a04bdbf31a2 100644 (file)
--- a/Doc/whatsnew/3.8.rst
+++ b/Doc/whatsnew/3.8.rst
@@ -1265,6 +1265,15 @@ Changes in the C API
 
   (Contributed by Zackery Spytz in :issue:`33407`.)
 
+* The interpreter does not pretend to support binary compatibility of
+  extension types accross feature releases, anymore.  A :c:type:`PyTypeObject`
+  exported by a third-party extension module is supposed to have all the
+  slots expected in the current Python version, including
+  :c:member:`~PyTypeObject.tp_finalize` (:const:`Py_TPFLAGS_HAVE_FINALIZE`
+  is not checked anymore before reading :c:member:`~PyTypeObject.tp_finalize`).
+
+  (Contributed by Antoine Pitrou in :issue:`32388`.)
+
 
 CPython bytecode changes
 ------------------------

diff --git a/Include/object.h b/Include/object.h
index 11ba2bb8e2388c1ca131198a14bb75b6c3f6b868..cc98d8a1def7e7ab56d4702992c00b6bd591aa57 100644 (file)
--- a/Include/object.h
+++ b/Include/object.h
@@ -263,17 +263,14 @@ PyAPI_FUNC(void) Py_ReprLeave(PyObject *);
 #define Py_PRINT_RAW    1       /* No string quotes etc. */
 
 /*
-`Type flags (tp_flags)
+Type flags (tp_flags)
 
-These flags are used to extend the type structure in a backwards-compatible
-fashion. Extensions can use the flags to indicate (and test) when a given
-type structure contains a new feature. The Python core will use these when
-introducing new functionality between major revisions (to avoid mid-version
-changes in the PYTHON_API_VERSION).
+These flags are used to change expected features and behavior for a
+particular type.
 
 Arbitration of the flag bit positions will need to be coordinated among
 all extension writers who publicly release their extensions (this will
-be fewer than you might expect!)..
+be fewer than you might expect!).
 
 Most flags were removed as of Python 3.0 to make room for new flags.  (Some
 flags are not for backwards compatibility but to indicate the presence of an
@@ -302,7 +299,7 @@ given type object has a specified feature.
 /* Set while the type is being 'readied', to prevent recursive ready calls */
 #define Py_TPFLAGS_READYING (1UL << 13)
 
-/* Objects support garbage collection (see objimp.h) */
+/* Objects support garbage collection (see objimpl.h) */
 #define Py_TPFLAGS_HAVE_GC (1UL << 14)
 
 /* These two bits are preserved for Stackless Python, next after this is 17 */
@@ -340,6 +337,11 @@ given type object has a specified feature.
 /* NOTE: The following flags reuse lower bits (removed as part of the
  * Python 3.0 transition). */
 
+/* The following flag is kept for compatibility.  Starting with 3.8,
+ * binary compatibility of C extensions accross feature releases of
+ * Python is not supported anymore, except when using the stable ABI.
+ */
+
 /* Type structure has tp_finalize member (3.4) */
 #define Py_TPFLAGS_HAVE_FINALIZE (1UL << 0)
 

diff --git a/Misc/NEWS.d/next/Core and Builtins/2017-12-21-20-37-40.bpo-32388.6w-i5t.rst b/Misc/NEWS.d/next/Core and Builtins/2017-12-21-20-37-40.bpo-32388.6w-i5t.rst
new file mode 100644 (file)
index 0000000..60615d4
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2017-12-21-20-37-40.bpo-32388.6w-i5t.rst
@@ -0,0 +1 @@
+Remove cross-version binary compatibility requirement in tp_flags.

diff --git a/Modules/_asynciomodule.c b/Modules/_asynciomodule.c
index 60136082a7eecfe9ff327bae1b3d7acfb3a66631..d8b631b7c7a2923d72db5c1dc76b23d1ae06775a 100644 (file)
--- a/Modules/_asynciomodule.c
+++ b/Modules/_asynciomodule.c
@@ -1430,8 +1430,7 @@ static PyTypeObject FutureType = {
     .tp_dealloc = FutureObj_dealloc,
     .tp_as_async = &FutureType_as_async,
     .tp_repr = (reprfunc)FutureObj_repr,
-    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,
+    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE,
     .tp_doc = _asyncio_Future___init____doc__,
     .tp_traverse = (traverseproc)FutureObj_traverse,
     .tp_clear = (inquiry)FutureObj_clear,
@@ -2461,8 +2460,7 @@ static PyTypeObject TaskType = {
     .tp_dealloc = TaskObj_dealloc,
     .tp_as_async = &FutureType_as_async,
     .tp_repr = (reprfunc)FutureObj_repr,
-    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,
+    .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE,
     .tp_doc = _asyncio_Task___init____doc__,
     .tp_traverse = (traverseproc)TaskObj_traverse,
     .tp_clear = (inquiry)TaskObj_clear,

diff --git a/Modules/_io/bufferedio.c b/Modules/_io/bufferedio.c
index 6f855b9edd08428f8aaf0f0cfa38463b903d261e..9c0eeb56860eea23b814a3d2ca9ac8accc7a4108 100644 (file)
--- a/Modules/_io/bufferedio.c
+++ b/Modules/_io/bufferedio.c
@@ -2342,8 +2342,7 @@ PyTypeObject PyBufferedIOBase_Type = {
     0,                          /*tp_getattro*/
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,  /*tp_flags*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
     bufferediobase_doc,         /* tp_doc */
     0,                          /* tp_traverse */
     0,                          /* tp_clear */
@@ -2434,7 +2433,7 @@ PyTypeObject PyBufferedReader_Type = {
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     _io_BufferedReader___init____doc__, /* tp_doc */
     (traverseproc)buffered_traverse, /* tp_traverse */
     (inquiry)buffered_clear,    /* tp_clear */
@@ -2520,7 +2519,7 @@ PyTypeObject PyBufferedWriter_Type = {
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,   /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     _io_BufferedWriter___init____doc__, /* tp_doc */
     (traverseproc)buffered_traverse, /* tp_traverse */
     (inquiry)buffered_clear,    /* tp_clear */
@@ -2597,7 +2596,7 @@ PyTypeObject PyBufferedRWPair_Type = {
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,   /* tp_flags */
+        | Py_TPFLAGS_HAVE_GC,   /* tp_flags */
     _io_BufferedRWPair___init____doc__, /* tp_doc */
     (traverseproc)bufferedrwpair_traverse, /* tp_traverse */
     (inquiry)bufferedrwpair_clear, /* tp_clear */
@@ -2691,7 +2690,7 @@ PyTypeObject PyBufferedRandom_Type = {
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,   /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     _io_BufferedRandom___init____doc__, /* tp_doc */
     (traverseproc)buffered_traverse, /* tp_traverse */
     (inquiry)buffered_clear,    /* tp_clear */

diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 52a6f49e1d325b38c034a3c4d17fe932e9767a9b..582a8130f622af1b4001a28682b9e5ff41ecb3d9 100644 (file)
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -1200,12 +1200,12 @@ PyTypeObject PyFileIO_Type = {
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,       /* tp_flags */
+        | Py_TPFLAGS_HAVE_GC,                   /* tp_flags */
     _io_FileIO___init____doc__,                 /* tp_doc */
     (traverseproc)fileio_traverse,              /* tp_traverse */
     (inquiry)fileio_clear,                      /* tp_clear */
     0,                                          /* tp_richcompare */
-    offsetof(fileio, weakreflist),      /* tp_weaklistoffset */
+    offsetof(fileio, weakreflist),              /* tp_weaklistoffset */
     0,                                          /* tp_iter */
     0,                                          /* tp_iternext */
     fileio_methods,                             /* tp_methods */
@@ -1215,7 +1215,7 @@ PyTypeObject PyFileIO_Type = {
     0,                                          /* tp_dict */
     0,                                          /* tp_descr_get */
     0,                                          /* tp_descr_set */
-    offsetof(fileio, dict),         /* tp_dictoffset */
+    offsetof(fileio, dict),                     /* tp_dictoffset */
     _io_FileIO___init__,                        /* tp_init */
     PyType_GenericAlloc,                        /* tp_alloc */
     fileio_new,                                 /* tp_new */

diff --git a/Modules/_io/iobase.c b/Modules/_io/iobase.c
index a5727b8deed35aabba7210d707546942e919bc95..8c8112d10f0ba865cba7dbe3d324ae9f4f3a0c9a 100644 (file)
--- a/Modules/_io/iobase.c
+++ b/Modules/_io/iobase.c
@@ -856,7 +856,7 @@ PyTypeObject PyIOBase_Type = {
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,   /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     iobase_doc,                 /* tp_doc */
     (traverseproc)iobase_traverse, /* tp_traverse */
     (inquiry)iobase_clear,      /* tp_clear */
@@ -1051,7 +1051,7 @@ PyTypeObject PyRawIOBase_Type = {
     0,                          /*tp_getattro*/
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_FINALIZE,  /*tp_flags*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
     rawiobase_doc,              /* tp_doc */
     0,                          /* tp_traverse */
     0,                          /* tp_clear */

diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index a08ab5b0e27ff6efeecec3c03ec66ded02625fea..3eb0dcc865ba2e7558f29f7f4fce3ec3d37b3b69 100644 (file)
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -183,8 +183,7 @@ PyTypeObject PyTextIOBase_Type = {
     0,                          /*tp_getattro*/
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,  /*tp_flags*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,  /*tp_flags*/
     textiobase_doc,             /* tp_doc */
     0,                          /* tp_traverse */
     0,                          /* tp_clear */
@@ -3258,7 +3257,7 @@ PyTypeObject PyTextIOWrapper_Type = {
     0,                          /*tp_setattro*/
     0,                          /*tp_as_buffer*/
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
+        | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
     _io_TextIOWrapper___init____doc__, /* tp_doc */
     (traverseproc)textiowrapper_traverse, /* tp_traverse */
     (inquiry)textiowrapper_clear, /* tp_clear */

diff --git a/Modules/_io/winconsoleio.c b/Modules/_io/winconsoleio.c
index 70a723ed746a75c2e491425a4ab9933629485e01..7700bd5b7c0d316f9fa0ace2ae29283df6c7ce38 100644 (file)
--- a/Modules/_io/winconsoleio.c
+++ b/Modules/_io/winconsoleio.c
@@ -1133,7 +1133,7 @@ PyTypeObject PyWindowsConsoleIO_Type = {
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,       /* tp_flags */
+        | Py_TPFLAGS_HAVE_GC,                   /* tp_flags */
     _io__WindowsConsoleIO___init____doc__,      /* tp_doc */
     (traverseproc)winconsoleio_traverse,        /* tp_traverse */
     (inquiry)winconsoleio_clear,                /* tp_clear */

diff --git a/Modules/_testmultiphase.c b/Modules/_testmultiphase.c
index db5bb7d6b8a22d8fc4d20c7501809b2f55cce250..4933abbabbe307e6178df2db7df8100d22439aec 100644 (file)
--- a/Modules/_testmultiphase.c
+++ b/Modules/_testmultiphase.c
@@ -98,7 +98,7 @@ static PyType_Spec Example_Type_spec = {
     "_testimportexec.Example",
     sizeof(ExampleObject),
     0,
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,
     Example_Type_slots
 };
 

diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 3b15c7ba5b6284629082797b292017d97a3a266a..0cf00e839661f08b3668168e247aa9ed62184005 100644 (file)
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -858,7 +858,6 @@ finalize_garbage(PyGC_Head *collectable)
         PyObject *op = FROM_GC(gc);
         gc_list_move(gc, &seen);
         if (!_PyGCHead_FINALIZED(gc) &&
-                PyType_HasFeature(Py_TYPE(op), Py_TPFLAGS_HAVE_FINALIZE) &&
                 (finalize = Py_TYPE(op)->tp_finalize) != NULL) {
             _PyGCHead_SET_FINALIZED(gc);
             Py_INCREF(op);

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index a3d979c3bcd78d72fa62d3b305eec4a80adb31bc..a25ff7a895c01d705ac5ab243e603922bdeec2fd 100644 (file)
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -13032,8 +13032,7 @@ static PyTypeObject ScandirIteratorType = {
     0,                                      /* tp_getattro */
     0,                                      /* tp_setattro */
     0,                                      /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT
-        | Py_TPFLAGS_HAVE_FINALIZE,         /* tp_flags */
+    Py_TPFLAGS_DEFAULT,                     /* tp_flags */
     0,                                      /* tp_doc */
     0,                                      /* tp_traverse */
     0,                                      /* tp_clear */

diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 74cdc0f2f6caed5aec4e942521ecd8a90dd1fc32..ca4d760f8cb4f423ab015499b4becf27120d1615 100644 (file)
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -5286,8 +5286,7 @@ static PyTypeObject sock_type = {
     PyObject_GenericGetAttr,                    /* tp_getattro */
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_FINALIZE,             /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,   /* tp_flags */
     sock_doc,                                   /* tp_doc */
     0,                                          /* tp_traverse */
     0,                                          /* tp_clear */

diff --git a/Modules/xxlimited.c b/Modules/xxlimited.c
index 190f9937d0de9f404e197d1191e78c97f5e3df1c..ffc04e0310e392780625b13d62a850aaa66078e5 100644 (file)
--- a/Modules/xxlimited.c
+++ b/Modules/xxlimited.c
@@ -123,7 +123,7 @@ static PyType_Spec Xxo_Type_spec = {
     "xxlimited.Xxo",
     sizeof(XxoObject),
     0,
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE,
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,
     Xxo_Type_slots
 };
 

diff --git a/Objects/genobject.c b/Objects/genobject.c
index e2def38af541a55fd7351d58c11c13444d00bc84..0d0a02d76ccf21f5269273db2f72187bc5eb35f1 100644 (file)
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -742,8 +742,7 @@ PyTypeObject PyGen_Type = {
     PyObject_GenericGetAttr,                    /* tp_getattro */
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
-        Py_TPFLAGS_HAVE_FINALIZE,               /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,    /* tp_flags */
     0,                                          /* tp_doc */
     (traverseproc)gen_traverse,                 /* tp_traverse */
     0,                                          /* tp_clear */
@@ -997,8 +996,7 @@ PyTypeObject PyCoro_Type = {
     PyObject_GenericGetAttr,                    /* tp_getattro */
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
-        Py_TPFLAGS_HAVE_FINALIZE,               /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,    /* tp_flags */
     0,                                          /* tp_doc */
     (traverseproc)gen_traverse,                 /* tp_traverse */
     0,                                          /* tp_clear */
@@ -1394,8 +1392,7 @@ PyTypeObject PyAsyncGen_Type = {
     PyObject_GenericGetAttr,                    /* tp_getattro */
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
-        Py_TPFLAGS_HAVE_FINALIZE,               /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,    /* tp_flags */
     0,                                          /* tp_doc */
     (traverseproc)async_gen_traverse,           /* tp_traverse */
     0,                                          /* tp_clear */

diff --git a/Objects/object.c b/Objects/object.c
index 87dba9898e3a8a36d32dbb5d531db2973c5b6b27..f9c75b7c6a4e95d574e7446c6e788a395bc07817 100644 (file)
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -298,10 +298,7 @@ PyObject_CallFinalizer(PyObject *self)
 {
     PyTypeObject *tp = Py_TYPE(self);
 
-    /* The former could happen on heaptypes created from the C API, e.g.
-       PyType_FromSpec(). */
-    if (!PyType_HasFeature(tp, Py_TPFLAGS_HAVE_FINALIZE) ||
-        tp->tp_finalize == NULL)
+    if (tp->tp_finalize == NULL)
         return;
     /* tp_finalize should only be called once. */
     if (PyType_IS_GC(tp) && _PyGC_FINALIZED(self))

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index c14cbad875b4437bbd1606132964e73bd03d1558..071ff27d532397af0524cc62b84174c1e7d5c5c7 100644 (file)
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -248,8 +248,8 @@ PyType_Modified(PyTypeObject *type)
        Invariants:
 
        - Py_TPFLAGS_VALID_VERSION_TAG is never set if
-         Py_TPFLAGS_HAVE_VERSION_TAG is not set (e.g. on type
-         objects coming from non-recompiled extension modules)
+         Py_TPFLAGS_HAVE_VERSION_TAG is not set (in case of a
+         bizarre MRO, see type_mro_modified()).
 
        - before Py_TPFLAGS_VALID_VERSION_TAG can be set on a type,
          it must first be set on all super types.
@@ -2571,7 +2571,7 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
 
     /* Initialize tp_flags */
     type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HEAPTYPE |
-        Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_FINALIZE;
+        Py_TPFLAGS_BASETYPE;
     if (base->tp_flags & Py_TPFLAGS_HAVE_GC)
         type->tp_flags |= Py_TPFLAGS_HAVE_GC;
 
@@ -5179,10 +5179,7 @@ inherit_slots(PyTypeObject *type, PyTypeObject *base)
         COPYSLOT(tp_init);
         COPYSLOT(tp_alloc);
         COPYSLOT(tp_is_gc);
-        if ((type->tp_flags & Py_TPFLAGS_HAVE_FINALIZE) &&
-            (base->tp_flags & Py_TPFLAGS_HAVE_FINALIZE)) {
-            COPYSLOT(tp_finalize);
-        }
+        COPYSLOT(tp_finalize);
         if ((type->tp_flags & Py_TPFLAGS_HAVE_GC) ==
             (base->tp_flags & Py_TPFLAGS_HAVE_GC)) {
             /* They agree about gc. */