bpo-46571: improve typing.no_type_check to skip foreign objects

sobolevn · sobolevn · commit a03009cb9520 · 2022-02-01T11:54:17.000+03:00
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst
@@ -1999,8 +1999,8 @@ Functions and decorators
    Decorator to indicate that annotations are not type hints.
 
    This works as class or function :term:`decorator`.  With a class, it
-   applies recursively to all methods defined in that class (but not
-   to methods defined in its superclasses or subclasses).
+   applies recursively to all methods and classes defined in that class
+   (but not to methods defined in its superclasses or subclasses).
 
    This mutates the function(s) in place.
 
diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
@@ -2965,9 +2965,73 @@ def meth(self, x: int): ...
         @no_type_check
         class D(C):
             c = C
+
         # verify that @no_type_check never affects bases
         self.assertEqual(get_type_hints(C.meth), {'x': int})
 
+        # and never child classes:
+        class Child(D):
+            def foo(self, x: int): ...
+
+        self.assertEqual(get_type_hints(Child.foo), {'x': int})
+
+    def test_no_type_check_nested_types(self):
+        # See https://bugs.python.org/issue46571
+        class Other:
+            o: int
+        class B:  # Has the same `__name__`` as `A.B` and different `__qualname__`
+            o: int
+        @no_type_check
+        class A:
+            a: int
+            class B:
+                b: int
+                class C:
+                    c: int
+            class D:
+                d: int
+
+            Other = Other
+
+        for klass in [A, A.B, A.B.C, A.D]:
+            with self.subTest(klass=klass):
+                self.assertTrue(klass.__no_type_check__)
+                self.assertEqual(get_type_hints(klass), {})
+
+        for not_modified in [Other, B]:
+            with self.subTest(not_modified=not_modified):
+                with self.assertRaises(AttributeError):
+                    not_modified.__no_type_check__
+                self.assertNotEqual(get_type_hints(not_modified), {})
+
+    def test_no_type_check_foreign_functions(self):
+        # We should not modify this function:
+        def some(*args: int) -> int:
+            ...
+
+        @no_type_check
+        class A:
+            some_alias = some
+            some_class = classmethod(some)
+            some_static = staticmethod(some)
+
+        with self.assertRaises(AttributeError):
+            some.__no_type_check__
+
+    def test_no_type_check_lambda(self):
+        @no_type_check
+        class A:
+            # Corner case: `lambda` is both an assignment and a function:
+            bar: Callable[[int], int] = lambda arg: arg
+
+        self.assertTrue(A.bar.__no_type_check__)
+        self.assertEqual(get_type_hints(A.bar), {})
+
+    def test_no_type_check_TypeError(self):
+        # This simply should not fail with
+        # `TypeError: can't set attributes of built-in/extension type 'dict'`
+        no_type_check(dict)
+
     def test_no_type_check_forward_ref_as_string(self):
         class C:
             foo: typing.ClassVar[int] = 7
diff --git a/Lib/typing.py b/Lib/typing.py
@@ -1959,11 +1959,13 @@ def no_type_check(arg):
     This mutates the function(s) or class(es) in place.
     """
     if isinstance(arg, type):
-        arg_attrs = arg.__dict__.copy()
-        for attr, val in arg.__dict__.items():
-            if val in arg.__bases__ + (arg,):
-                arg_attrs.pop(attr)
-        for obj in arg_attrs.values():
+        for obj in arg.__dict__.values():
+            if (hasattr(obj, '__qualname__')
+                    and obj.__qualname__ != f'{arg.__qualname__}.{obj.__name__}'):
+                # We only modify objects that are defined in this type directly.
+                # If classes / methods are nested in multiple layers,
+                # we will modify them when processing their direct holders.
+                continue
             if isinstance(obj, types.FunctionType):
                 obj.__no_type_check__ = True
             if isinstance(obj, type):
diff --git a/Misc/NEWS.d/next/Library/2022-02-01-11-21-34.bpo-46571.L40xUJ.rst b/Misc/NEWS.d/next/Library/2022-02-01-11-21-34.bpo-46571.L40xUJ.rst
@@ -0,0 +1,2 @@
+Improve :func:`typing.no_type_check` to not modify foreign functions and
+types.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Improve :func:`typing.no_type_check` to not modify foreign functions and
	`2`	`+types.`