bpo-34909: keep searching mixins until base class is found (GH-9737) (GH-9738)

(cherry picked from commit cd45385ffa)

Lib/enum.py

@@ -455,7 +455,7 @@ class EnumMeta(type):
                     if base is object:
                         continue
                     elif '__new__' in base.__dict__:
-                        if issubclass(base, Enum) and not hasattr(base, '__new_member__'):
+                        if issubclass(base, Enum):
                             continue
                         return base
 
@@ -468,7 +468,6 @@ class EnumMeta(type):
         member_type = _find_data_type(bases) or object
         if first_enum._member_names_:
             raise TypeError("Cannot extend enumerations")
-
         return member_type, first_enum
 
     @staticmethod
@@ -514,7 +513,6 @@ class EnumMeta(type):
             use_args = False
         else:
             use_args = True
-
         return __new__, save_new, use_args
 
 

Lib/test/test_enum.py

@@ -1813,6 +1813,27 @@ class TestEnum(unittest.TestCase):
         self.assertEqual(ConfusedColor.RED.social(), "what's up?")
         self.assertTrue(issubclass(ReformedColor, int))
 
+    def test_multiple_inherited_mixin(self):
+        class StrEnum(str, Enum):
+            def __new__(cls, *args, **kwargs):
+                for a in args:
+                    if not isinstance(a, str):
+                        raise TypeError("Enumeration '%s' (%s) is not"
+                                        " a string" % (a, type(a).__name__))
+                return str.__new__(cls, *args, **kwargs)
+        @unique
+        class Decision1(StrEnum):
+            REVERT = "REVERT"
+            REVERT_ALL = "REVERT_ALL"
+            RETRY = "RETRY"
+        class MyEnum(StrEnum):
+            pass
+        @unique
+        class Decision2(MyEnum):
+            REVERT = "REVERT"
+            REVERT_ALL = "REVERT_ALL"
+            RETRY = "RETRY"
+
 
 class TestOrder(unittest.TestCase):