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gh-124153: Implement `PyType_GetBaseByToken()` and `Py_tp_token` slot… · python/cpython@646f16b · GitHub

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gh-124153: Implement PyType_GetBaseByToken() and Py_tp_token slot (GH-124163)
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Lines changed: 443 additions & 13 deletions

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‎Doc/c-api/type.rst‎

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@@ -264,6 +264,24 @@ Type Objects
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.. versionadded:: 3.11
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.. c:function:: int PyType_GetBaseByToken(PyTypeObject *type, void *token, PyTypeObject **result)
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Find the first superclass in *type*'s :term:`method resolution order` whose
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:c:macro:`Py_tp_token` token is equal to the given one.
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* If found, set *\*result* to a new :term:`strong reference`
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to it and return ``1``.
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* If not found, set *\*result* to ``NULL`` and return ``0``.
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* On error, set *\*result* to ``NULL`` and return ``-1`` with an
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exception set.
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The *result* argument may be ``NULL``, in which case *\*result* is not set.
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Use this if you need only the return value.
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The *token* argument may not be ``NULL``.
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.. versionadded:: 3.14
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.. c:function:: int PyUnstable_Type_AssignVersionTag(PyTypeObject *type)
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Attempt to assign a version tag to the given type.
@@ -488,6 +506,11 @@ The following functions and structs are used to create
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* ``Py_nb_add`` to set :c:member:`PyNumberMethods.nb_add`
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* ``Py_sq_length`` to set :c:member:`PySequenceMethods.sq_length`
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An additional slot is supported that does not correspond to a
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:c:type:`!PyTypeObject` struct field:
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* :c:data:`Py_tp_token`
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The following “offset” fields cannot be set using :c:type:`PyType_Slot`:
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* :c:member:`~PyTypeObject.tp_weaklistoffset`
@@ -538,4 +561,47 @@ The following functions and structs are used to create
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The desired value of the slot. In most cases, this is a pointer
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to a function.
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Slots other than ``Py_tp_doc`` may not be ``NULL``.
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*pfunc* values may not be ``NULL``, except for the following slots:
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* ``Py_tp_doc``
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* :c:data:`Py_tp_token` (for clarity, prefer :c:data:`Py_TP_USE_SPEC`
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rather than ``NULL``)
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.. c:macro:: Py_tp_token
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A :c:member:`~PyType_Slot.slot` that records a static memory layout ID
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for a class.
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If the :c:type:`PyType_Spec` of the class is statically
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allocated, the token can be set to the spec using the special value
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:c:data:`Py_TP_USE_SPEC`:
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.. code-block:: c
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static PyType_Slot foo_slots[] = {
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{Py_tp_token, Py_TP_USE_SPEC},
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It can also be set to an arbitrary pointer, but you must ensure that:
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* The pointer outlives the class, so it's not reused for something else
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while the class exists.
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* It "belongs" to the extension module where the class lives, so it will not
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clash with other extensions.
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Use :c:func:`PyType_GetBaseByToken` to check if a class's superclass has
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a given token -- that is, check whether the memory layout is compatible.
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To get the token for a given class (without considering superclasses),
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use :c:func:`PyType_GetSlot` with ``Py_tp_token``.
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.. versionadded:: 3.14
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.. c:namespace:: NULL
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.. c:macro:: Py_TP_USE_SPEC
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Used as a value with :c:data:`Py_tp_token` to set the token to the
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class's :c:type:`PyType_Spec`.
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Expands to ``NULL``.
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.. versionadded:: 3.14

‎Doc/data/stable_abi.dat‎

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‎Doc/whatsnew/3.14.rst‎

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@@ -554,6 +554,11 @@ New Features
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(Contributed by Victor Stinner in :gh:`107954`.)
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* Add :c:func:`PyType_GetBaseByToken` and :c:data:`Py_tp_token` slot for easier
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superclass identification, which attempts to resolve the `type checking issue
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<https://peps.python.org/pep-0630/#type-checking>`__ mentioned in :pep:`630`
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(:gh:`124153`).
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Porting to Python 3.14
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----------------------

‎Include/cpython/object.h‎

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@@ -269,6 +269,7 @@ typedef struct _heaptypeobject {
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struct _dictkeysobject *ht_cached_keys;
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PyObject *ht_module;
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char *_ht_tpname; // Storage for "tp_name"; see PyType_FromModuleAndSpec
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void *ht_token; // Storage for the "Py_tp_token" slot
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struct _specialization_cache _spec_cache; // For use by the specializer.
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#ifdef Py_GIL_DISABLED
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Py_ssize_t unique_id; // ID used for thread-local refcounting

‎Include/object.h‎

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@@ -391,6 +391,10 @@ PyAPI_FUNC(PyObject *) PyType_FromMetaclass(PyTypeObject*, PyObject*, PyType_Spe
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PyAPI_FUNC(void *) PyObject_GetTypeData(PyObject *obj, PyTypeObject *cls);
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PyAPI_FUNC(Py_ssize_t) PyType_GetTypeDataSize(PyTypeObject *cls);
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#endif
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#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030E0000
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PyAPI_FUNC(int) PyType_GetBaseByToken(PyTypeObject *, void *, PyTypeObject **);
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#define Py_TP_USE_SPEC NULL
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#endif
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/* Generic type check */
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PyAPI_FUNC(int) PyType_IsSubtype(PyTypeObject *, PyTypeObject *);

‎Include/typeslots.h‎

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@@ -90,3 +90,7 @@
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/* New in 3.14 */
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#define Py_tp_vectorcall 82
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#endif
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#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030E0000
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/* New in 3.14 */
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#define Py_tp_token 83
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#endif

‎Lib/test/test_capi/test_misc.py‎

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@@ -1144,6 +1144,77 @@ class MyType:
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MyType.__module__ = 123
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self.assertEqual(get_type_fullyqualname(MyType), 'my_qualname')
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def test_get_base_by_token(self):
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def get_base_by_token(src, key, comparable=True):
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def run(use_mro):
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find_first = _testcapi.pytype_getbasebytoken
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ret1, result = find_first(src, key, use_mro, True)
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ret2, no_result = find_first(src, key, use_mro, False)
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self.assertIn(ret1, (0, 1))
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self.assertEqual(ret1, result is not None)
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self.assertEqual(ret1, ret2)
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self.assertIsNone(no_result)
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return result
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found_in_mro = run(True)
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found_in_bases = run(False)
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if comparable:
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self.assertIs(found_in_mro, found_in_bases)
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return found_in_mro
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return found_in_mro, found_in_bases
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create_type = _testcapi.create_type_with_token
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get_token = _testcapi.get_tp_token
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Py_TP_USE_SPEC = _testcapi.Py_TP_USE_SPEC
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self.assertEqual(Py_TP_USE_SPEC, 0)
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A1 = create_type('_testcapi.A1', Py_TP_USE_SPEC)
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self.assertTrue(get_token(A1) != Py_TP_USE_SPEC)
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B1 = create_type('_testcapi.B1', id(self))
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self.assertTrue(get_token(B1) == id(self))
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tokenA1 = get_token(A1)
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# find A1 from A1
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found = get_base_by_token(A1, tokenA1)
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self.assertIs(found, A1)
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# no token in static types
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STATIC = type(1)
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self.assertEqual(get_token(STATIC), 0)
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found = get_base_by_token(STATIC, tokenA1)
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self.assertIs(found, None)
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# no token in pure subtypes
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class A2(A1): pass
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self.assertEqual(get_token(A2), 0)
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# find A1
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class Z(STATIC, B1, A2): pass
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found = get_base_by_token(Z, tokenA1)
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self.assertIs(found, A1)
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# searching for NULL token is an error
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with self.assertRaises(SystemError):
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get_base_by_token(Z, 0)
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with self.assertRaises(SystemError):
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get_base_by_token(STATIC, 0)
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# share the token with A1
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C1 = create_type('_testcapi.C1', tokenA1)
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self.assertTrue(get_token(C1) == tokenA1)
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# find C1 first by shared token
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class Z(C1, A2): pass
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found = get_base_by_token(Z, tokenA1)
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self.assertIs(found, C1)
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# B1 not found
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found = get_base_by_token(Z, get_token(B1))
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self.assertIs(found, None)
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with self.assertRaises(TypeError):
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_testcapi.pytype_getbasebytoken(
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'not a type', id(self), True, False)
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def test_gen_get_code(self):
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def genf(): yield

‎Lib/test/test_stable_abi_ctypes.py‎

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‎Lib/test/test_sys.py‎

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@@ -1718,7 +1718,7 @@ def delx(self): del self.__x
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'3P' # PyMappingMethods
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'10P' # PySequenceMethods
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'2P' # PyBufferProcs
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'6P'
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'7P'
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'1PIP' # Specializer cache
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+ typeid # heap type id (free-threaded only)
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)

‎Misc/NEWS.d/next/C_API/2024-09-17-05-23-35.gh-issue-124153.L8TWmx.rst‎

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@@ -0,0 +1,2 @@
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Add :c:func:`PyType_GetBaseByToken` and :c:data:`Py_tp_token` slot for easier
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type checking, related to :pep:`489` and :pep:`630`.

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