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gh-93274: Make vectorcall safe on mutable classes & inherit it by default (#95437)
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‎Doc/c-api/call.rst

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@@ -57,6 +57,15 @@ This bears repeating:
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A class supporting vectorcall **must** also implement
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:c:member:`~PyTypeObject.tp_call` with the same semantics.
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.. versionchanged:: 3.12
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The :const:`Py_TPFLAGS_HAVE_VECTORCALL` flag is now removed from a class
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when the class's :py:meth:`~object.__call__` method is reassigned.
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(This internally sets :c:member:`~PyTypeObject.tp_call` only, and thus
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may make it behave differently than the vectorcall function.)
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In earlier Python versions, vectorcall should only be used with
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:const:`immutable <Py_TPFLAGS_IMMUTABLETYPE>` or static types.
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A class should not implement vectorcall if that would be slower
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than *tp_call*. For example, if the callee needs to convert
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the arguments to an args tuple and kwargs dict anyway, then there is no point

‎Doc/c-api/typeobj.rst

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@@ -720,29 +720,29 @@ and :c:type:`PyType_Type` effectively act as defaults.)
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with the *vectorcallfunc* function.
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This can be done by setting *tp_call* to :c:func:`PyVectorcall_Call`.
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.. warning::
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It is not recommended for :ref:`mutable heap types <heap-types>` to implement
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the vectorcall protocol.
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When a user sets :attr:`__call__` in Python code, only *tp_call* is updated,
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likely making it inconsistent with the vectorcall function.
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.. versionchanged:: 3.8
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Before version 3.8, this slot was named ``tp_print``.
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In Python 2.x, it was used for printing to a file.
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In Python 3.0 to 3.7, it was unused.
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.. versionchanged:: 3.12
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Before version 3.12, it was not recommended for
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:ref:`mutable heap types <heap-types>` to implement the vectorcall
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protocol.
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When a user sets :attr:`~type.__call__` in Python code, only *tp_call* is
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updated, likely making it inconsistent with the vectorcall function.
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Since 3.12, setting ``__call__`` will disable vectorcall optimization
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by clearing the :const:`Py_TPFLAGS_HAVE_VECTORCALL` flag.
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**Inheritance:**
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This field is always inherited.
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However, the :const:`Py_TPFLAGS_HAVE_VECTORCALL` flag is not
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always inherited. If it's not, then the subclass won't use
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always inherited. If it's not set, then the subclass won't use
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:ref:`vectorcall <vectorcall>`, except when
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:c:func:`PyVectorcall_Call` is explicitly called.
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This is in particular the case for types without the
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:const:`Py_TPFLAGS_IMMUTABLETYPE` flag set (including subclasses defined in
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Python).
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.. c:member:: getattrfunc PyTypeObject.tp_getattr
@@ -1178,12 +1178,18 @@ and :c:type:`PyType_Type` effectively act as defaults.)
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**Inheritance:**
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This bit is inherited for types with the
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:const:`Py_TPFLAGS_IMMUTABLETYPE` flag set, if
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:c:member:`~PyTypeObject.tp_call` is also inherited.
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This bit is inherited if :c:member:`~PyTypeObject.tp_call` is also
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inherited.
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.. versionadded:: 3.9
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.. versionchanged:: 3.12
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This flag is now removed from a class when the class's
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:py:meth:`~object.__call__` method is reassigned.
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This flag can now be inherited by mutable classes.
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.. data:: Py_TPFLAGS_IMMUTABLETYPE
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This bit is set for type objects that are immutable: type attributes cannot be set nor deleted.

‎Doc/whatsnew/3.12.rst

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@@ -414,6 +414,15 @@ New Features
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an additional metaclass argument.
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(Contributed by Wenzel Jakob in :gh:`93012`.)
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* (XXX: this should be combined with :gh:`93274` when that is done)
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The :const:`Py_TPFLAGS_HAVE_VECTORCALL` flag is now removed from a class
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when the class's :py:meth:`~object.__call__` method is reassigned.
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This makes vectorcall safe to use with mutable types (i.e. heap types
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without the :const:`immutable <Py_TPFLAGS_IMMUTABLETYPE>` flag).
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Mutable types that do not override :c:member:`~PyTypeObject.tp_call` now
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inherit the :const:`Py_TPFLAGS_HAVE_VECTORCALL` flag.
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(Contributed by Petr Viktorin in :gh:`93012`.)
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Porting to Python 3.12
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----------------------
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‎Lib/test/test_call.py

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@@ -606,9 +606,19 @@ def test_vectorcall_flag(self):
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self.assertFalse(_testcapi.MethodDescriptorNopGet.__flags__ & Py_TPFLAGS_HAVE_VECTORCALL)
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self.assertTrue(_testcapi.MethodDescriptor2.__flags__ & Py_TPFLAGS_HAVE_VECTORCALL)
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# Mutable heap types should not inherit Py_TPFLAGS_HAVE_VECTORCALL
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# Mutable heap types should inherit Py_TPFLAGS_HAVE_VECTORCALL,
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# but should lose it when __call__ is overridden
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class MethodDescriptorHeap(_testcapi.MethodDescriptorBase):
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pass
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self.assertTrue(MethodDescriptorHeap.__flags__ & Py_TPFLAGS_HAVE_VECTORCALL)
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MethodDescriptorHeap.__call__ = print
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self.assertFalse(MethodDescriptorHeap.__flags__ & Py_TPFLAGS_HAVE_VECTORCALL)
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# Mutable heap types should not inherit Py_TPFLAGS_HAVE_VECTORCALL if
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# they define __call__ directly
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class MethodDescriptorHeap(_testcapi.MethodDescriptorBase):
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def __call__(self):
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pass
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self.assertFalse(MethodDescriptorHeap.__flags__ & Py_TPFLAGS_HAVE_VECTORCALL)
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def test_vectorcall_override(self):
@@ -621,6 +631,58 @@ def test_vectorcall_override(self):
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f = _testcapi.MethodDescriptorNopGet()
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self.assertIs(f(*args), args)
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def test_vectorcall_override_on_mutable_class(self):
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"""Setting __call__ should disable vectorcall"""
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TestType = _testcapi.make_vectorcall_class()
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instance = TestType()
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self.assertEqual(instance(), "tp_call")
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instance.set_vectorcall(TestType)
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self.assertEqual(instance(), "vectorcall") # assume vectorcall is used
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TestType.__call__ = lambda self: "custom"
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self.assertEqual(instance(), "custom")
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def test_vectorcall_override_with_subclass(self):
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"""Setting __call__ on a superclass should disable vectorcall"""
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SuperType = _testcapi.make_vectorcall_class()
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class DerivedType(SuperType):
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pass
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instance = DerivedType()
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# Derived types with its own vectorcall should be unaffected
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UnaffectedType1 = _testcapi.make_vectorcall_class(DerivedType)
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UnaffectedType2 = _testcapi.make_vectorcall_class(SuperType)
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# Aside: Quickly check that the C helper actually made derived types
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self.assertTrue(issubclass(UnaffectedType1, DerivedType))
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self.assertTrue(issubclass(UnaffectedType2, SuperType))
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# Initial state: tp_call
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self.assertEqual(instance(), "tp_call")
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self.assertEqual(_testcapi.has_vectorcall_flag(SuperType), True)
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self.assertEqual(_testcapi.has_vectorcall_flag(DerivedType), True)
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self.assertEqual(_testcapi.has_vectorcall_flag(UnaffectedType1), True)
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self.assertEqual(_testcapi.has_vectorcall_flag(UnaffectedType2), True)
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# Setting the vectorcall function
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instance.set_vectorcall(SuperType)
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self.assertEqual(instance(), "vectorcall")
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self.assertEqual(_testcapi.has_vectorcall_flag(SuperType), True)
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self.assertEqual(_testcapi.has_vectorcall_flag(DerivedType), True)
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self.assertEqual(_testcapi.has_vectorcall_flag(UnaffectedType1), True)
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self.assertEqual(_testcapi.has_vectorcall_flag(UnaffectedType2), True)
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# Setting __call__ should remove vectorcall from all subclasses
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SuperType.__call__ = lambda self: "custom"
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self.assertEqual(instance(), "custom")
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self.assertEqual(_testcapi.has_vectorcall_flag(SuperType), False)
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self.assertEqual(_testcapi.has_vectorcall_flag(DerivedType), False)
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self.assertEqual(_testcapi.has_vectorcall_flag(UnaffectedType1), True)
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self.assertEqual(_testcapi.has_vectorcall_flag(UnaffectedType2), True)
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def test_vectorcall(self):
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# Test a bunch of different ways to call objects:
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# 1. vectorcall using PyVectorcall_Call()

‎Misc/NEWS.d/next/C API/2022-07-29-15-24-45.gh-issue-93012.-DdGEy.rst

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@@ -0,0 +1,6 @@
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The :const:`Py_TPFLAGS_HAVE_VECTORCALL` flag is now removed from a class
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when the class's :py:meth:`~object.__call__` method is reassigned. This
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makes vectorcall safe to use with mutable types (i.e. heap types without the
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:const:`immutable <Py_TPFLAGS_IMMUTABLETYPE>` flag). Mutable types that do
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not override :c:member:`~PyTypeObject.tp_call` now inherit the
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:const:`Py_TPFLAGS_HAVE_VECTORCALL` flag.

‎Modules/_testcapi/clinic/vectorcall.c.h

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