gh-115539: Allow enum.Flag to have None members

Author: Jason-Y-Z

Lib/enum.py

@@ -279,9 +279,10 @@ def __set_name__(self, enum_class, member_name):
         enum_member._sort_order_ = len(enum_class._member_names_)
 
         if Flag is not None and issubclass(enum_class, Flag):
-            enum_class._flag_mask_ |= value
-            if _is_single_bit(value):
-                enum_class._singles_mask_ |= value
+            if isinstance(value, int):
+                enum_class._flag_mask_ |= value
+                if _is_single_bit(value):
+                    enum_class._singles_mask_ |= value
             enum_class._all_bits_ = 2 ** ((enum_class._flag_mask_).bit_length()) - 1
 
         # If another member with the same value was already defined, the
@@ -309,6 +310,7 @@ def __set_name__(self, enum_class, member_name):
             elif (
                     Flag is not None
                     and issubclass(enum_class, Flag)
+                    and isinstance(value, int)
                     and _is_single_bit(value)
                 ):
                 # no other instances found, record this member in _member_names_

Lib/test/test_enum.py

@@ -1047,6 +1047,14 @@ class TestPlainEnumFunction(_EnumTests, _PlainOutputTests, unittest.TestCase):
 
 class TestPlainFlagClass(_EnumTests, _PlainOutputTests, _FlagTests, unittest.TestCase):
     enum_type = Flag
+    
+    def test_none_member(self):
+        class FlagWithNoneMember(Flag):
+            A = 1
+            E = None
+        
+        self.assertEqual(FlagWithNoneMember.A.value, 1)
+        self.assertIs(FlagWithNoneMember.E.value, None)
 
 
 class TestPlainFlagFunction(_EnumTests, _PlainOutputTests, _FlagTests, unittest.TestCase):