bpo-46469: Make asyncio generic classes return GenericAlias (GH-30777)

* bpo-46469: Make asyncio generic classes return GenericAlias

* 📜🤖 Added by blurb_it.

* Update Misc/NEWS.d/next/Library/2022-01-22-05-05-08.bpo-46469.plUab5.rst

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Lib/asyncio/futures.py

@@ -8,6 +8,7 @@ import concurrent.futures
 import contextvars
 import logging
 import sys
+from types import GenericAlias
 
 from . import base_futures
 from . import events
@@ -106,8 +107,7 @@ class Future:
             context['source_traceback'] = self._source_traceback
         self._loop.call_exception_handler(context)
 
-    def __class_getitem__(cls, type):
-        return cls
+    __class_getitem__ = classmethod(GenericAlias)
 
     @property
     def _log_traceback(self):

Lib/asyncio/queues.py

@@ -2,6 +2,7 @@ __all__ = ('Queue', 'PriorityQueue', 'LifoQueue', 'QueueFull', 'QueueEmpty')
 
 import collections
 import heapq
+from types import GenericAlias
 
 from . import locks
 from . import mixins
@@ -69,8 +70,7 @@ class Queue(mixins._LoopBoundMixin):
     def __str__(self):
         return f'<{type(self).__name__} {self._format()}>'
 
-    def __class_getitem__(cls, type):
-        return cls
+    __class_getitem__ = classmethod(GenericAlias)
 
     def _format(self):
         result = f'maxsize={self._maxsize!r}'

Lib/asyncio/tasks.py

@@ -17,6 +17,7 @@ import itertools
 import types
 import warnings
 import weakref
+from types import GenericAlias
 
 from . import base_tasks
 from . import coroutines
@@ -123,8 +124,7 @@ class Task(futures._PyFuture):  # Inherit Python Task implementation
             self._loop.call_exception_handler(context)
         super().__del__()
 
-    def __class_getitem__(cls, type):
-        return cls
+    __class_getitem__ = classmethod(GenericAlias)
 
     def _repr_info(self):
         return base_tasks._task_repr_info(self)

Lib/test/test_asyncio/test_futures.py

@@ -7,7 +7,7 @@ import sys
 import threading
 import unittest
 from unittest import mock
-
+from types import GenericAlias
 import asyncio
 from asyncio import futures
 from test.test_asyncio import utils as test_utils
@@ -109,6 +109,11 @@ class BaseFutureTests:
         self.loop = self.new_test_loop()
         self.addCleanup(self.loop.close)
 
+    def test_generic_alias(self):
+        future = self.cls[str]
+        self.assertEqual(future.__args__, (str,))
+        self.assertIsInstance(future, GenericAlias)
+
     def test_isfuture(self):
         class MyFuture:
             _asyncio_future_blocking = None

Lib/test/test_asyncio/test_queues.py

@@ -1,9 +1,8 @@
 """Tests for queues.py"""
 
 import unittest
-from unittest import mock
-
 import asyncio
+from types import GenericAlias
 from test.test_asyncio import utils as test_utils
 
 
@@ -74,6 +73,11 @@ class QueueBasicTests(_QueueTestBase):
     def test_str(self):
         self._test_repr_or_str(str, False)
 
+    def test_generic_alias(self):
+        q = asyncio.Queue[int]
+        self.assertEqual(q.__args__, (int,))
+        self.assertIsInstance(q, GenericAlias)
+
     def test_empty(self):
         q = asyncio.Queue()
         self.assertTrue(q.empty())

Lib/test/test_asyncio/test_tasks.py

@@ -11,10 +11,10 @@ import re
 import sys
 import textwrap
 import traceback
-import types
 import unittest
 import weakref
 from unittest import mock
+from types import GenericAlias
 
 import asyncio
 from asyncio import coroutines
@@ -108,6 +108,12 @@ class BaseTaskTests:
         self.loop.set_task_factory(self.new_task)
         self.loop.create_future = lambda: self.new_future(self.loop)
 
+
+    def test_generic_alias(self):
+        task = self.__class__.Task[str]
+        self.assertEqual(task.__args__, (str,))
+        self.assertIsInstance(task, GenericAlias)
+
     def test_task_cancel_message_getter(self):
         async def coro():
             pass

Misc/NEWS.d/next/Library/2022-01-22-05-05-08.bpo-46469.plUab5.rst

@@ -0,0 +1 @@
+:mod:`asyncio` generic classes now return :class:`types.GenericAlias` in ``__class_getitem__`` instead of the same class.

Modules/_asynciomodule.c

@@ -1480,13 +1480,6 @@ finally:
     PyErr_Restore(error_type, error_value, error_traceback);
 }
 
-static PyObject *
-future_cls_getitem(PyObject *cls, PyObject *type)
-{
-    Py_INCREF(cls);
-    return cls;
-}
-
 static PyAsyncMethods FutureType_as_async = {
     (unaryfunc)future_new_iter,         /* am_await */
     0,                                  /* am_aiter */
@@ -1507,7 +1500,7 @@ static PyMethodDef FutureType_methods[] = {
     _ASYNCIO_FUTURE_GET_LOOP_METHODDEF
     _ASYNCIO_FUTURE__MAKE_CANCELLED_ERROR_METHODDEF
     _ASYNCIO_FUTURE__REPR_INFO_METHODDEF
-    {"__class_getitem__", future_cls_getitem, METH_O|METH_CLASS, NULL},
+    {"__class_getitem__", Py_GenericAlias, METH_O|METH_CLASS, PyDoc_STR("See PEP 585")},
     {NULL, NULL}        /* Sentinel */
 };
 
@@ -2449,13 +2442,6 @@ done:
     FutureObj_finalize((FutureObj*)task);
 }
 
-static PyObject *
-task_cls_getitem(PyObject *cls, PyObject *type)
-{
-    Py_INCREF(cls);
-    return cls;
-}
-
 static void TaskObj_dealloc(PyObject *);  /* Needs Task_CheckExact */
 
 static PyMethodDef TaskType_methods[] = {
@@ -2475,7 +2461,7 @@ static PyMethodDef TaskType_methods[] = {
     _ASYNCIO_TASK_GET_NAME_METHODDEF
     _ASYNCIO_TASK_SET_NAME_METHODDEF
     _ASYNCIO_TASK_GET_CORO_METHODDEF
-    {"__class_getitem__", task_cls_getitem, METH_O|METH_CLASS, NULL},
+    {"__class_getitem__", Py_GenericAlias, METH_O|METH_CLASS, PyDoc_STR("See PEP 585")},
     {NULL, NULL}        /* Sentinel */
 };