typing.TypeAliasType compatibility

src/test_typing_extensions.py

@@ -7439,6 +7439,15 @@ def test_type_var_tuple_compatibility(self):
         T6 = TypeAliasType("TypingTypeVarTuple", ..., type_params=(typingTs,))
         self.assertEqual(T6.__type_params__, (typingTs,))
 
+    @skipUnless(TYPING_3_12_0, "typing.TypeAliasType is not available before 3.12")
+    def test_isinstance_compatibility(self):
+        typing_TA = typing.TypeAliasType("typing_TA", int)
+        ns = {}
+        exec("type Int = int", None, ns)
+        self.assertTrue(isinstance(typing_TA, TypeAliasType))
+        self.assertTrue(isinstance(ns["Int"], TypeAliasType))
+
+
     def test_type_params_possibilities(self):
         T = TypeVar('T')
         # Test not a tuple

src/typing_extensions.py

@@ -3572,7 +3572,16 @@ def __getitem__(self, item):
                     result.__class__ = type(self)
                     return result
 
-    class TypeAliasType:
+    class _TypeAliasTypeMeta(type):
+        # 3.12+
+        if hasattr(typing, "TypeAliasType"):
+            def __instancecheck__(cls, instance):
+                return (
+                    cls.__class__ == TypeAliasType
+                    or isinstance(instance, typing.TypeAliasType)
+                )
+
+    class TypeAliasType(metaclass=_TypeAliasTypeMeta):
         """Create named, parameterized type aliases.
 
         This provides a backport of the new `type` statement in Python 3.12: