bpo-39481: Implementation for PEP 585 (#18239)

This implements things like `list[int]`,
which returns an object of type `types.GenericAlias`.
This object mostly acts as a proxy for `list`,
but has attributes `__origin__` and `__args__`
that allow recovering the parts (with values `list` and `(int,)`.

There is also an approximate notion of type variables;
e.g. `list[T]` has a `__parameters__` attribute equal to `(T,)`.
Type variables are objects of type `typing.TypeVar`.

1 files changed, 3 insertions, 2 deletions

diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py
index 524ab7c..f4cba0f 100644
--- a/Lib/test/test_tempfile.py
+++ b/Lib/test/test_tempfile.py
@@ -10,6 +10,7 @@ import re
 import warnings
 import contextlib
 import stat
+import types
 import weakref
 from unittest import mock
 
@@ -1222,8 +1223,8 @@ class TestSpooledTemporaryFile(BaseTestCase):
         self.assertEqual(os.fstat(f.fileno()).st_size, 20)
 
     def test_class_getitem(self):
-        self.assertIs(tempfile.SpooledTemporaryFile[bytes],
-                      tempfile.SpooledTemporaryFile)
+        self.assertIsInstance(tempfile.SpooledTemporaryFile[bytes],
+                      types.GenericAlias)
 
 if tempfile.NamedTemporaryFile is not tempfile.TemporaryFile: