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bpo-32388: Remove cross-version binary compatibility requirement in tp_flags (pythonGH-4944)
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.
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-51
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‎Doc/c-api/typeobj.rst

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@@ -1099,6 +1099,11 @@ and :c:type:`PyType_Type` effectively act as defaults.)
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.. versionadded:: 3.4
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.. deprecated:: 3.8
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This flag isn't necessary anymore, as the interpreter assumes the
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:c:member:`~PyTypeObject.tp_finalize` slot is always present in the
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type structure.
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.. c:member:: const char* PyTypeObject.tp_doc
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‎Doc/whatsnew/3.8.rst

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

‎Include/object.h

Lines changed: 10 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -263,17 +263,14 @@ PyAPI_FUNC(void) Py_ReprLeave(PyObject *);
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#define Py_PRINT_RAW 1 /* No string quotes etc. */
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/*
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`Type flags (tp_flags)
266+
Type flags (tp_flags)
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268-
These flags are used to extend the type structure in a backwards-compatible
269-
fashion. Extensions can use the flags to indicate (and test) when a given
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type structure contains a new feature. The Python core will use these when
271-
introducing new functionality between major revisions (to avoid mid-version
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changes in the PYTHON_API_VERSION).
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These flags are used to change expected features and behavior for a
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particular type.
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Arbitration of the flag bit positions will need to be coordinated among
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all extension writers who publicly release their extensions (this will
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be fewer than you might expect!)..
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be fewer than you might expect!).
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Most flags were removed as of Python 3.0 to make room for new flags. (Some
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flags are not for backwards compatibility but to indicate the presence of an
@@ -302,7 +299,7 @@ given type object has a specified feature.
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/* Set while the type is being 'readied', to prevent recursive ready calls */
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#define Py_TPFLAGS_READYING (1UL << 13)
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/* Objects support garbage collection (see objimp.h) */
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/* Objects support garbage collection (see objimpl.h) */
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#define Py_TPFLAGS_HAVE_GC (1UL << 14)
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/* These two bits are preserved for Stackless Python, next after this is 17 */
@@ -340,6 +337,11 @@ given type object has a specified feature.
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/* NOTE: The following flags reuse lower bits (removed as part of the
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* Python 3.0 transition). */
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340+
/* The following flag is kept for compatibility. Starting with 3.8,
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* binary compatibility of C extensions accross feature releases of
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* Python is not supported anymore, except when using the stable ABI.
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*/
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/* Type structure has tp_finalize member (3.4) */
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#define Py_TPFLAGS_HAVE_FINALIZE (1UL << 0)
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‎Misc/NEWS.d/next/Core and Builtins/2017-12-21-20-37-40.bpo-32388.6w-i5t.rst

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@@ -0,0 +1 @@
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Remove cross-version binary compatibility requirement in tp_flags.

‎Modules/_asynciomodule.c

Lines changed: 2 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1430,8 +1430,7 @@ static PyTypeObject FutureType = {
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.tp_dealloc = FutureObj_dealloc,
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.tp_as_async = &FutureType_as_async,
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.tp_repr = (reprfunc)FutureObj_repr,
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.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_FINALIZE,
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.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE,
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.tp_doc = _asyncio_Future___init____doc__,
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.tp_traverse = (traverseproc)FutureObj_traverse,
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.tp_clear = (inquiry)FutureObj_clear,
@@ -2461,8 +2460,7 @@ static PyTypeObject TaskType = {
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.tp_dealloc = TaskObj_dealloc,
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.tp_as_async = &FutureType_as_async,
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.tp_repr = (reprfunc)FutureObj_repr,
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.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_FINALIZE,
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.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_BASETYPE,
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.tp_doc = _asyncio_Task___init____doc__,
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.tp_traverse = (traverseproc)TaskObj_traverse,
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.tp_clear = (inquiry)TaskObj_clear,

‎Modules/_io/bufferedio.c

Lines changed: 5 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -2342,8 +2342,7 @@ PyTypeObject PyBufferedIOBase_Type = {
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0, /*tp_getattro*/
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
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bufferediobase_doc, /* tp_doc */
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0, /* tp_traverse */
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0, /* tp_clear */
@@ -2434,7 +2433,7 @@ PyTypeObject PyBufferedReader_Type = {
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
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| Py_TPFLAGS_HAVE_GC, /*tp_flags*/
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_io_BufferedReader___init____doc__, /* tp_doc */
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(traverseproc)buffered_traverse, /* tp_traverse */
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(inquiry)buffered_clear, /* tp_clear */
@@ -2520,7 +2519,7 @@ PyTypeObject PyBufferedWriter_Type = {
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
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| Py_TPFLAGS_HAVE_GC, /*tp_flags*/
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_io_BufferedWriter___init____doc__, /* tp_doc */
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(traverseproc)buffered_traverse, /* tp_traverse */
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(inquiry)buffered_clear, /* tp_clear */
@@ -2597,7 +2596,7 @@ PyTypeObject PyBufferedRWPair_Type = {
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /* tp_flags */
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| Py_TPFLAGS_HAVE_GC, /* tp_flags */
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_io_BufferedRWPair___init____doc__, /* tp_doc */
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(traverseproc)bufferedrwpair_traverse, /* tp_traverse */
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(inquiry)bufferedrwpair_clear, /* tp_clear */
@@ -2691,7 +2690,7 @@ PyTypeObject PyBufferedRandom_Type = {
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
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| Py_TPFLAGS_HAVE_GC, /*tp_flags*/
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_io_BufferedRandom___init____doc__, /* tp_doc */
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(traverseproc)buffered_traverse, /* tp_traverse */
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(inquiry)buffered_clear, /* tp_clear */

‎Modules/_io/fileio.c

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@@ -1200,12 +1200,12 @@ PyTypeObject PyFileIO_Type = {
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0, /* tp_setattro */
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0, /* tp_as_buffer */
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /* tp_flags */
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| Py_TPFLAGS_HAVE_GC, /* tp_flags */
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_io_FileIO___init____doc__, /* tp_doc */
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(traverseproc)fileio_traverse, /* tp_traverse */
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(inquiry)fileio_clear, /* tp_clear */
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0, /* tp_richcompare */
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offsetof(fileio, weakreflist), /* tp_weaklistoffset */
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offsetof(fileio, weakreflist), /* tp_weaklistoffset */
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0, /* tp_iter */
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0, /* tp_iternext */
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fileio_methods, /* tp_methods */
@@ -1215,7 +1215,7 @@ PyTypeObject PyFileIO_Type = {
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0, /* tp_dict */
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0, /* tp_descr_get */
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0, /* tp_descr_set */
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offsetof(fileio, dict), /* tp_dictoffset */
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offsetof(fileio, dict), /* tp_dictoffset */
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_io_FileIO___init__, /* tp_init */
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PyType_GenericAlloc, /* tp_alloc */
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fileio_new, /* tp_new */

‎Modules/_io/iobase.c

Lines changed: 2 additions & 2 deletions
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@@ -856,7 +856,7 @@ PyTypeObject PyIOBase_Type = {
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
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| Py_TPFLAGS_HAVE_GC, /*tp_flags*/
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iobase_doc, /* tp_doc */
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(traverseproc)iobase_traverse, /* tp_traverse */
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(inquiry)iobase_clear, /* tp_clear */
@@ -1051,7 +1051,7 @@ PyTypeObject PyRawIOBase_Type = {
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0, /*tp_getattro*/
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
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rawiobase_doc, /* tp_doc */
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0, /* tp_traverse */
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0, /* tp_clear */

‎Modules/_io/textio.c

Lines changed: 2 additions & 3 deletions
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@@ -183,8 +183,7 @@ PyTypeObject PyTextIOBase_Type = {
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0, /*tp_getattro*/
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
186-
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
187-
| Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
186+
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /*tp_flags*/
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textiobase_doc, /* tp_doc */
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0, /* tp_traverse */
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0, /* tp_clear */
@@ -3258,7 +3257,7 @@ PyTypeObject PyTextIOWrapper_Type = {
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0, /*tp_setattro*/
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0, /*tp_as_buffer*/
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
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| Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /*tp_flags*/
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| Py_TPFLAGS_HAVE_GC, /*tp_flags*/
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_io_TextIOWrapper___init____doc__, /* tp_doc */
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(traverseproc)textiowrapper_traverse, /* tp_traverse */
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(inquiry)textiowrapper_clear, /* tp_clear */

‎Modules/_io/winconsoleio.c

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@@ -1133,7 +1133,7 @@ PyTypeObject PyWindowsConsoleIO_Type = {
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0, /* tp_setattro */
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0, /* tp_as_buffer */
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Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
1136-
| Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_HAVE_FINALIZE, /* tp_flags */
1136+
| Py_TPFLAGS_HAVE_GC, /* tp_flags */
11371137
_io__WindowsConsoleIO___init____doc__, /* tp_doc */
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(traverseproc)winconsoleio_traverse, /* tp_traverse */
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(inquiry)winconsoleio_clear, /* tp_clear */

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