bpo-45684: Add __class_getitem__ method to singledispatchmethod

Lib/functools.py

@@ -923,6 +923,8 @@ def _method(*args, **kwargs):
     def __isabstractmethod__(self):
         return getattr(self.func, '__isabstractmethod__', False)
 
+    __class_getitem__ = classmethod(GenericAlias)
+
 
 ################################################################################
 ### cached_property() - computed once per instance, cached as attribute

Lib/test/test_genericalias.py

@@ -12,7 +12,9 @@
 from contextlib import AbstractContextManager, AbstractAsyncContextManager
 from contextvars import ContextVar, Token
 from dataclasses import Field
-from functools import partial, partialmethod, cached_property
+from functools import (
+    partial, partialmethod, cached_property, singledispatchmethod
+)
 from mailbox import Mailbox, _PartialFile
 try:
     import ctypes
@@ -55,7 +57,8 @@ class BaseTest(unittest.TestCase):
                      FileInput,
                      OrderedDict, Counter, UserDict, UserList,
                      Pattern, Match,
-                     partial, partialmethod, cached_property,
+                     partial, partialmethod,
+                     cached_property, singledispatchmethod,
                      AbstractContextManager, AbstractAsyncContextManager,
                      Awaitable, Coroutine,
                      AsyncIterable, AsyncIterator,

Misc/NEWS.d/next/Library/2021-11-01-22-40-18.bpo-45684.4mkten.rst

@@ -0,0 +1 @@
+Add ``__class_getitem__`` method to ``functools.singledispatchmethod``.