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carljm · Feb 9, 2024 · 0cee0a6 · 0cee0a6
1 parent 88ca12a
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diff --git 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
@@ -0,0 +1,2 @@
+Fix "issubclass() arg 1 must be a class" errors in certain cases of multiple
+inheritance with generic aliases.