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_subprocess.py b/Lib/test/test_subprocess.py
index 7cf31e1..aced876 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -11,6 +11,7 @@ import errno
 import tempfile
 import time
 import traceback
+import types
 import selectors
 import sysconfig
 import select
@@ -1435,8 +1436,8 @@ class ProcessTestCase(BaseTestCase):
         self.assertEqual(c.exception.filename, '/some/nonexistent/directory')
 
     def test_class_getitems(self):
-        self.assertIs(subprocess.Popen[bytes], subprocess.Popen)
-        self.assertIs(subprocess.CompletedProcess[str], subprocess.CompletedProcess)
+        self.assertIsInstance(subprocess.Popen[bytes], types.GenericAlias)
+        self.assertIsInstance(subprocess.CompletedProcess[str], types.GenericAlias)
 
 class RunFuncTestCase(BaseTestCase):
     def run_python(self, code, **kwargs):