Implement typing_extensions.Any (#68)

CHANGELOG.md

@@ -1,3 +1,8 @@
+# Release 4.4.0 ()
+- Add `typing_extensions.Any` a backport of python 3.11's Any class which is
+  subclassable at runtime. (backport from python/cpython#31841, by Shantanu 
+  and Jelle Zijlstra). Patch by James Hilton-Balfe (@Gobot1234).
+
 # Release 4.3.0 (July 1, 2022)
 
 - Add `typing_extensions.NamedTuple`, allowing for generic `NamedTuple`s on

src/test_typing_extensions.py

@@ -15,13 +15,13 @@
 from unittest.mock import patch
 from test import ann_module, ann_module2, ann_module3
 import typing
-from typing import TypeVar, Optional, Union, Any, AnyStr
+from typing import TypeVar, Optional, Union, AnyStr
 from typing import T, KT, VT  # Not in __all__.
 from typing import Tuple, List, Dict, Iterable, Iterator, Callable
 from typing import Generic
 from typing import no_type_check
 import typing_extensions
-from typing_extensions import NoReturn, ClassVar, Final, IntVar, Literal, Type, NewType, TypedDict, Self
+from typing_extensions import NoReturn, Any, ClassVar, Final, IntVar, Literal, Type, NewType, TypedDict, Self
 from typing_extensions import TypeAlias, ParamSpec, Concatenate, ParamSpecArgs, ParamSpecKwargs, TypeGuard
 from typing_extensions import Awaitable, AsyncIterator, AsyncContextManager, Required, NotRequired
 from typing_extensions import Protocol, runtime, runtime_checkable, Annotated, final, is_typeddict
@@ -160,6 +160,48 @@ def test_exception(self):
             assert_never(None)
 
 
+class AnyTests(BaseTestCase):
+    def test_can_subclass(self):
+        class Mock(Any): pass
+        self.assertTrue(issubclass(Mock, Any))
+        self.assertIsInstance(Mock(), Mock)
+
+        class Something: pass
+        self.assertFalse(issubclass(Something, Any))
+        self.assertNotIsInstance(Something(), Mock)
+
+        class MockSomething(Something, Mock): pass
+        self.assertTrue(issubclass(MockSomething, Any))
+        ms = MockSomething()
+        self.assertIsInstance(ms, MockSomething)
+        self.assertIsInstance(ms, Something)
+        self.assertIsInstance(ms, Mock)
+
+    class SubclassesAny(Any):
+        ...
+
+    def test_repr(self):
+        if sys.version_info >= (3, 11):
+            mod_name = 'typing'
+        else:
+            mod_name = 'typing_extensions'
+        self.assertEqual(repr(Any), f"{mod_name}.Any")
+        if sys.version_info < (3, 11):  # skip for now on 3.11+ see python/cpython#95987
+            self.assertEqual(repr(self.SubclassesAny), "<class 'test_typing_extensions.AnyTests.SubclassesAny'>")
+
+    def test_instantiation(self):
+        with self.assertRaises(TypeError):
+            Any()
+
+        self.SubclassesAny()
+
+    def test_isinstance(self):
+        with self.assertRaises(TypeError):
+            isinstance(object(), Any)
+
+        isinstance(object(), self.SubclassesAny)
+
+
 class ClassVarTests(BaseTestCase):
 
     def test_basics(self):
@@ -3018,7 +3060,7 @@ def test_typing_extensions_defers_when_possible(self):
         if sys.version_info < (3, 10):
             exclude |= {'get_args', 'get_origin'}
         if sys.version_info < (3, 11):
-            exclude |= {'final', 'NamedTuple'}
+            exclude |= {'final', 'NamedTuple', 'Any'}
         for item in typing_extensions.__all__:
             if item not in exclude and hasattr(typing, item):
                 self.assertIs(

src/typing_extensions.py

@@ -11,6 +11,7 @@
 # Please keep __all__ alphabetized within each category.
 __all__ = [
     # Super-special typing primitives.
+    'Any',
     'ClassVar',
     'Concatenate',
     'Final',
@@ -149,6 +150,37 @@ def _collect_type_vars(types, typevar_types=None):
 T_co = typing.TypeVar('T_co', covariant=True)  # Any type covariant containers.
 T_contra = typing.TypeVar('T_contra', contravariant=True)  # Ditto contravariant.
 
+
+if sys.version_info >= (3, 11):
+    from typing import Any
+else:
+
+    class _AnyMeta(type):
+        def __instancecheck__(self, obj):
+            if self is Any:
+                raise TypeError("typing_extensions.Any cannot be used with isinstance()")
+            return super().__instancecheck__(obj)
+
+        def __repr__(self):
+            if self is Any:
+                return "typing_extensions.Any"
+            return super().__repr__()
+
+    class Any(metaclass=_AnyMeta):
+        """Special type indicating an unconstrained type.
+        - Any is compatible with every type.
+        - Any assumed to have all methods.
+        - All values assumed to be instances of Any.
+        Note that all the above statements are true from the point of view of
+        static type checkers. At runtime, Any should not be used with instance
+        checks.
+        """
+        def __new__(cls, *args, **kwargs):
+            if cls is Any:
+                raise TypeError("Any cannot be instantiated")
+            return super().__new__(cls, *args, **kwargs)
+
+
 ClassVar = typing.ClassVar
 
 # On older versions of typing there is an internal class named "Final".