From 0cee0a662c28aa3021e3c18eb6ab7b3474b3f796 Mon Sep 17 00:00:00 2001
From: Carl Meyer <carl@oddbird.net>
Date: Thu, 8 Feb 2024 17:06:06 -0800
Subject: [PATCH] add news entry and comment

---
 Lib/typing.py                                                  | 3 +++
 .../Library/2024-02-08-17-04-58.gh-issue-112903.SN_vUs.rst     | 2 ++
 2 files changed, 5 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2024-02-08-17-04-58.gh-issue-112903.SN_vUs.rst

diff --git a/Lib/typing.py b/Lib/typing.py
index 71680221541991..3e533fb0f56cfd 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1136,6 +1136,9 @@ def __mro_entries__(self, bases):
         if self.__origin__ not in bases:
             res.append(self.__origin__)
         i = bases.index(self)
+        # The goal here is to only add Generic to the MRO if nothing else in the
+        # MRO is already a subclass of Generic; otherwise we risk failure to
+        # linearize a consistent MRO.
         for b in bases[i+1:]:
             if isinstance(b, _BaseGenericAlias):
                 break
diff --git a/Misc/NEWS.d/next/Library/2024-02-08-17-04-58.gh-issue-112903.SN_vUs.rst b/Misc/NEWS.d/next/Library/2024-02-08-17-04-58.gh-issue-112903.SN_vUs.rst
new file mode 100644
index 00000000000000..1d65e767551008
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-02-08-17-04-58.gh-issue-112903.SN_vUs.rst
@@ -0,0 +1,2 @@
+Fix "issubclass() arg 1 must be a class" errors in certain cases of multiple
+inheritance with generic aliases.