pythongh-104003: Implement PEP 702

Author: JelleZijlstra

Lib/test/test_typing.py

@@ -23,7 +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 override, deprecated
 from typing import is_typeddict
 from typing import reveal_type
 from typing import dataclass_transform
@@ -4699,6 +4699,152 @@ def on_bottom(self, a: int) -> int:
         self.assertTrue(instance.on_bottom.__override__)
 
 
+class DeprecatedTests(BaseTestCase):
+    def test_dunder_deprecated(self):
+        @deprecated("A will go away soon")
+        class A:
+            pass
+
+        self.assertEqual(A.__deprecated__, "A will go away soon")
+        self.assertIsInstance(A, type)
+
+        @deprecated("b will go away soon")
+        def b():
+            pass
+
+        self.assertEqual(b.__deprecated__, "b will go away soon")
+        self.assertIsInstance(b, types.FunctionType)
+
+        @overload
+        @deprecated("no more ints")
+        def h(x: int) -> int: ...
+        @overload
+        def h(x: str) -> str: ...
+        def h(x):
+            return x
+
+        overloads = get_overloads(h)
+        self.assertEqual(len(overloads), 2)
+        self.assertEqual(overloads[0].__deprecated__, "no more ints")
+
+    def test_class(self):
+        @deprecated("A will go away soon")
+        class A:
+            pass
+
+        with self.assertWarnsRegex(DeprecationWarning, "A will go away soon"):
+            A()
+        with self.assertRaises(TypeError), self.assertWarnsRegex(DeprecationWarning, "A will go away soon"):
+            A(42)
+
+        @deprecated("HasInit will go away soon")
+        class HasInit:
+            def __init__(self, x):
+                self.x = x
+
+        with self.assertWarnsRegex(DeprecationWarning, "HasInit will go away soon"):
+            instance = HasInit(42)
+        self.assertEqual(instance.x, 42)
+
+        has_new_called = False
+
+        @deprecated("HasNew will go away soon")
+        class HasNew:
+            def __new__(cls, x):
+                nonlocal has_new_called
+                has_new_called = True
+                return super().__new__(cls)
+
+            def __init__(self, x) -> None:
+                self.x = x
+
+        with self.assertWarnsRegex(DeprecationWarning, "HasNew will go away soon"):
+            instance = HasNew(42)
+        self.assertEqual(instance.x, 42)
+        self.assertTrue(has_new_called)
+        new_base_called = False
+
+        class NewBase:
+            def __new__(cls, x):
+                nonlocal new_base_called
+                new_base_called = True
+                return super().__new__(cls)
+
+            def __init__(self, x) -> None:
+                self.x = x
+
+        @deprecated("HasInheritedNew will go away soon")
+        class HasInheritedNew(NewBase):
+            pass
+
+        with self.assertWarnsRegex(DeprecationWarning, "HasInheritedNew will go away soon"):
+            instance = HasInheritedNew(42)
+        self.assertEqual(instance.x, 42)
+        self.assertTrue(new_base_called)
+
+    def test_function(self):
+        @deprecated("b will go away soon")
+        def b():
+            pass
+
+        with self.assertWarnsRegex(DeprecationWarning, "b will go away soon"):
+            b()
+
+    def test_method(self):
+        class Capybara:
+            @deprecated("x will go away soon")
+            def x(self):
+                pass
+
+        instance = Capybara()
+        with self.assertWarnsRegex(DeprecationWarning, "x will go away soon"):
+            instance.x()
+
+    def test_property(self):
+        class Capybara:
+            @property
+            @deprecated("x will go away soon")
+            def x(self):
+                pass
+
+            @property
+            def no_more_setting(self):
+                return 42
+
+            @no_more_setting.setter
+            @deprecated("no more setting")
+            def no_more_setting(self, value):
+                pass
+
+        instance = Capybara()
+        with self.assertWarnsRegex(DeprecationWarning, "x will go away soon"):
+            instance.x
+
+        with warnings.catch_warnings():
+            warnings.simplefilter("error")
+            self.assertEqual(instance.no_more_setting, 42)
+
+        with self.assertWarnsRegex(DeprecationWarning, "no more setting"):
+            instance.no_more_setting = 42
+
+    def test_category(self):
+        @deprecated("c will go away soon", category=RuntimeWarning)
+        def c():
+            pass
+
+        with self.assertWarnsRegex(RuntimeWarning, "c will go away soon"):
+            c()
+
+    def test_turn_off_warnings(self):
+        @deprecated("d will go away soon", category=None)
+        def d():
+            pass
+
+        with warnings.catch_warnings():
+            warnings.simplefilter("error")
+            d()
+
+
 class CastTests(BaseTestCase):
 
     def test_basics(self):

Lib/typing.py

@@ -124,6 +124,7 @@ def _idfunc(_, x):
     'cast',
     'clear_overloads',
     'dataclass_transform',
+    'deprecated',
     'final',
     'get_args',
     'get_origin',
@@ -3551,3 +3552,79 @@ def method(self) -> None:
         # read-only property, TypeError if it's a builtin class.
         pass
     return method
+
+
+def deprecated(
+    msg: str,
+    /,
+    *,
+    category: type[Warning] | None = DeprecationWarning,
+    stacklevel: int = 1,
+) -> Callable[[T], T]:
+    """Indicate that a class, function or overload is deprecated.
+
+    Usage:
+
+        @deprecated("Use B instead")
+        class A:
+            pass
+
+        @deprecated("Use g instead")
+        def f():
+            pass
+
+        @overload
+        @deprecated("int support is deprecated")
+        def g(x: int) -> int: ...
+        @overload
+        def g(x: str) -> int: ...
+
+    When this decorator is applied to an object, the type checker
+    will generate a diagnostic on usage of the deprecated object.
+
+    No runtime warning is issued. The decorator sets the ``__deprecated__``
+    attribute on the decorated object to the deprecation message
+    passed to the decorator. If applied to an overload, the decorator
+    must be after the ``@overload`` decorator for the attribute to
+    exist on the overload as returned by ``get_overloads()``.
+
+    See PEP 702 for details.
+
+    """
+    def decorator(arg: T, /) -> T:
+        if category is None:
+            arg.__deprecated__ = msg
+            return arg
+        elif isinstance(arg, type):
+            original_new = arg.__new__
+            has_init = arg.__init__ is not object.__init__
+
+            @functools.wraps(original_new)
+            def __new__(cls, *args, **kwargs):
+                warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
+                # Mirrors a similar check in object.__new__.
+                if not has_init and (args or kwargs):
+                    raise TypeError(f"{cls.__name__}() takes no arguments")
+                if original_new is not object.__new__:
+                    return original_new(cls, *args, **kwargs)
+                else:
+                    return original_new(cls)
+
+            arg.__new__ = staticmethod(__new__)
+            arg.__deprecated__ = __new__.__deprecated__ = msg
+            return arg
+        elif callable(arg):
+            @functools.wraps(arg)
+            def wrapper(*args, **kwargs):
+                warnings.warn(msg, category=category, stacklevel=stacklevel + 1)
+                return arg(*args, **kwargs)
+
+            arg.__deprecated__ = wrapper.__deprecated__ = msg
+            return wrapper
+        else:
+            raise TypeError(
+                "@deprecated decorator with non-None category must be applied to "
+                f"a class or callable, not {arg!r}"
+            )
+
+    return decorator