gh-104600: Make function.__type_params__ writable (#104601)

Lib/functools.py

@@ -30,7 +30,7 @@ from types import GenericAlias
 # wrapper functions that can handle naive introspection
 
 WRAPPER_ASSIGNMENTS = ('__module__', '__name__', '__qualname__', '__doc__',
-                       '__annotations__')
+                       '__annotations__', '__type_params__')
 WRAPPER_UPDATES = ('__dict__',)
 def update_wrapper(wrapper,
                    wrapped,

Lib/test/test_funcattrs.py

@@ -1,5 +1,6 @@
 import textwrap
 import types
+import typing
 import unittest
 
 
@@ -190,6 +191,20 @@ class FunctionPropertiesTest(FuncAttrsTest):
         # __qualname__ must be a string
         self.cannot_set_attr(self.b, '__qualname__', 7, TypeError)
 
+    def test___type_params__(self):
+        def generic[T](): pass
+        def not_generic(): pass
+        T, = generic.__type_params__
+        self.assertIsInstance(T, typing.TypeVar)
+        self.assertEqual(generic.__type_params__, (T,))
+        self.assertEqual(not_generic.__type_params__, ())
+        with self.assertRaises(TypeError):
+            del not_generic.__type_params__
+        with self.assertRaises(TypeError):
+            not_generic.__type_params__ = 42
+        not_generic.__type_params__ = (T,)
+        self.assertEqual(not_generic.__type_params__, (T,))
+
     def test___code__(self):
         num_one, num_two = 7, 8
         def a(): pass

Lib/test/test_functools.py

@@ -617,7 +617,7 @@ class TestUpdateWrapper(unittest.TestCase):
 
 
     def _default_update(self):
-        def f(a:'This is a new annotation'):
+        def f[T](a:'This is a new annotation'):
             """This is a test"""
             pass
         f.attr = 'This is also a test'
@@ -630,12 +630,14 @@ class TestUpdateWrapper(unittest.TestCase):
     def test_default_update(self):
         wrapper, f = self._default_update()
         self.check_wrapper(wrapper, f)
+        T, = f.__type_params__
         self.assertIs(wrapper.__wrapped__, f)
         self.assertEqual(wrapper.__name__, 'f')
         self.assertEqual(wrapper.__qualname__, f.__qualname__)
         self.assertEqual(wrapper.attr, 'This is also a test')
         self.assertEqual(wrapper.__annotations__['a'], 'This is a new annotation')
         self.assertNotIn('b', wrapper.__annotations__)
+        self.assertEqual(wrapper.__type_params__, (T,))
 
     @unittest.skipIf(sys.flags.optimize >= 2,
                      "Docstrings are omitted with -O2 and above")

Lib/test/test_type_params.py

@@ -843,5 +843,5 @@ class TypeParamsTypeParamsDunder(unittest.TestCase):
             func.__type_params__ = ()
         """
 
-        with self.assertRaisesRegex(AttributeError, "attribute '__type_params__' of 'function' objects is not writable"):
-            run_code(code)
+        ns = run_code(code)
+        self.assertEqual(ns["func"].__type_params__, ())