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Expand Up		@@ -91,6 +91,8 @@ annotations. These include:
		Introducing :data:`LiteralString`
		* :pep:`681`: Data Class Transforms
		Introducing the :func:`@dataclass_transform<dataclass_transform>` decorator
		* :pep:`698`: Adding an override decorator to typing
		Introducing the :func:`@override<override>` decorator

		.. _type-aliases:

Expand Down Expand Up		@@ -2722,6 +2724,42 @@ Functions and decorators
		This wraps the decorator with something that wraps the decorated
		function in :func:`no_type_check`.


		.. decorator:: override

		A decorator for methods that indicates to type checkers that this method
		should override a method or attribute with the same name on a base class.
		This helps prevent bugs that may occur when a base class is changed without
		an equivalent change to a child class.

		For example::

		class Base:
		def log_status(self)

		class Sub(Base):
		@override
		def log_status(self) -> None: # Okay: overrides Base.log_status
		...

		@override
		def done(self) -> None: # Error reported by type checker
		...

		There is no runtime checking of this property.

		The decorator will set the ``__override__`` attribute to ``True`` on
		the decorated object. Thus, a check like
		``if getattr(obj, "__override__", False)`` can be used at runtime to determine
		whether an object ``obj`` has been marked as an override. If the decorated object
		does not support setting attributes, the decorator returns the object unchanged
		without raising an exception.

		See :pep:`698` for more details.

		.. versionadded:: 3.12


		.. decorator:: type_check_only

		Decorator to mark a class or function to be unavailable at runtime.
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8 changes: 8 additions & 0 deletions 8 Doc/whatsnew/3.12.rst

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Expand Up		@@ -350,6 +350,14 @@ tempfile
		The :class:`tempfile.NamedTemporaryFile` function has a new optional parameter
		delete_on_close (Contributed by Evgeny Zorin in :gh:`58451`.)

		typing
		------

		* Add :func:`typing.override`, an override decorator telling to static type
		checkers to verify that a method overrides some method or attribute of the
		same name on a base class, as per :pep:`698`. (Contributed by Steven Troxler in
		:gh:`101564`.)

		sys
		---

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38 changes: 38 additions & 0 deletions 38 Lib/test/test_typing.py

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Expand Up		@@ -23,6 +23,7 @@
		from typing import assert_type, cast, runtime_checkable
		from typing import get_type_hints
		from typing import get_origin, get_args
		from typing import override
		from typing import is_typeddict
		from typing import reveal_type
		from typing import dataclass_transform
Expand Down Expand Up		@@ -4166,6 +4167,43 @@ def cached(self): ...
		self.assertIs(True, Methods.cached.__final__)


		class OverrideDecoratorTests(BaseTestCase):
		def test_override(self):
		class Base:
		def normal_method(self): ...
		@staticmethod
		def static_method_good_order(): ...
		@staticmethod
		def static_method_bad_order(): ...
		@staticmethod
		def decorator_with_slots(): ...

		class Derived(Base):
		@override
		def normal_method(self):
		return 42

		@staticmethod
		@override
		def static_method_good_order():
		return 42

		@override
		@staticmethod
		def static_method_bad_order():
		return 42


		self.assertIsSubclass(Derived, Base)
		instance = Derived()
		self.assertEqual(instance.normal_method(), 42)
		self.assertIs(True, instance.normal_method.__override__)
		self.assertEqual(Derived.static_method_good_order(), 42)
		self.assertIs(True, Derived.static_method_good_order.__override__)
		self.assertEqual(Derived.static_method_bad_order(), 42)
		self.assertIs(False, hasattr(Derived.static_method_bad_order, "__override__"))


		class CastTests(BaseTestCase):

		def test_basics(self):
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41 changes: 41 additions & 0 deletions 41 Lib/typing.py

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Expand Up		@@ -138,6 +138,7 @@ def _idfunc(_, x):
		'NoReturn',
		'NotRequired',
		'overload',
		'override',
		'ParamSpecArgs',
		'ParamSpecKwargs',
		'Required',
Expand Down Expand Up		@@ -2657,6 +2658,7 @@ class Other(Leaf): # Error reported by type checker
		# Internal type variable used for Type[].
		CT_co = TypeVar('CT_co', covariant=True, bound=type)


		# A useful type variable with constraints. This represents string types.
		# (This one is for export!)
		AnyStr = TypeVar('AnyStr', bytes, str)
Expand Down Expand Up		@@ -2748,6 +2750,8 @@ def new_user(user_class: Type[U]) -> U:
		At this point the type checker knows that joe has type BasicUser.
		"""

		# Internal type variable for callables. Not for export.
		F = TypeVar("F", bound=Callable[..., Any])

		@runtime_checkable
		class SupportsInt(Protocol):
Expand Down Expand Up		@@ -3448,3 +3452,40 @@ def decorator(cls_or_fn):
		}
		return cls_or_fn
		return decorator



		def override(method: F, /) -> F:
		"""Indicate that a method is intended to override a method in a base class.

		Usage:

		class Base:
		def method(self) -> None: ...
		pass

		class Child(Base):
		@override
		def method(self) -> None:
		super().method()

		When this decorator is applied to a method, the type checker will
		validate that it overrides a method or attribute with the same name on a
		base class. This helps prevent bugs that may occur when a base class is
		changed without an equivalent change to a child class.

		There is no runtime checking of this property. The decorator sets the
		``__override__`` attribute to ``True`` on the decorated object to allow
		runtime introspection.

		See PEP 698 for details.

		"""
		try:
		method.__override__ = True
		except (AttributeError, TypeError):
		# Skip the attribute silently if it is not writable.
		# AttributeError happens if the object has __slots__ or a
		# read-only property, TypeError if it's a builtin class.
		pass
		return method

1 change: 1 addition & 0 deletions 1 Misc/ACKS

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -1848,6 +1848,7 @@ Tom Tromey
		John Tromp
		Diane Trout
		Jason Trowbridge
		Steven Troxler
		Brent Tubbs
		Anthony Tuininga
		Erno Tukia
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1 change: 1 addition & 0 deletions 1 Misc/NEWS.d/next/Library/2023-02-04-16-35-46.gh-issue-101561.Xo6pIZ.rst

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Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Add a new decorator :func:`typing.override`. See :pep:`698` for details. Patch by Steven Troxler.

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