diff --git a/Doc/library/enum.rst b/Doc/library/enum.rst
index e8e4942..b354a11 100644
--- a/Doc/library/enum.rst
+++ b/Doc/library/enum.rst
@@ -1125,9 +1125,9 @@
 _Private__names
 """""""""""""""
 
-Private names will be normal attributes in Python 3.10 instead of either an error
+Private names will be normal attributes in Python 3.11 instead of either an error
 or a member (depending on if the name ends with an underscore). Using these names
-in 3.9 will issue a :exc:`DeprecationWarning`.
+in 3.10 will issue a :exc:`DeprecationWarning`.
 
 
 ``Enum`` member type
@@ -1150,6 +1150,10 @@
     >>> FieldTypes.size.value
     2
 
+.. note::
+
+   This behavior is deprecated and will be removed in 3.12.
+
 .. versionchanged:: 3.5
 
 
@@ -1200,3 +1204,9 @@
     >>> Color(7)      # not named combination
     <Color.CYAN|MAGENTA|BLUE|YELLOW|GREEN|RED: 7>
 
+.. note::
+
+   In 3.11 unnamed combinations of flags will only produce the canonical flag
+   members (aka single-value flags).  So ``Color(7)`` will produce something
+   like ``<Color.BLUE|GREEN|RED: 7>``.
+
diff --git a/Lib/enum.py b/Lib/enum.py
index db79e66..f5657a6 100644
--- a/Lib/enum.py
+++ b/Lib/enum.py
@@ -44,10 +44,11 @@ def _is_sunder(name):
 def _is_private(cls_name, name):
     # do not use `re` as `re` imports `enum`
     pattern = '_%s__' % (cls_name, )
+    pat_len = len(pattern)
     if (
-            len(name) >= 5
+            len(name) > pat_len
             and name.startswith(pattern)
-            and name[len(pattern)] != '_'
+            and name[pat_len:pat_len+1] != ['_']
             and (name[-1] != '_' or name[-2] != '_')
         ):
         return True
@@ -392,12 +393,19 @@ def __call__(cls, value, names=None, *, module=None, qualname=None, type=None, s
                 start=start,
                 )
 
-    def __contains__(cls, member):
-        if not isinstance(member, Enum):
+    def __contains__(cls, obj):
+        if not isinstance(obj, Enum):
+            import warnings
+            warnings.warn(
+                    "in 3.12 __contains__ will no longer raise TypeError, but will return True if\n"
+                    "obj is a member or a member's value",
+                    DeprecationWarning,
+                    stacklevel=2,
+                    )
             raise TypeError(
                 "unsupported operand type(s) for 'in': '%s' and '%s'" % (
-                    type(member).__qualname__, cls.__class__.__qualname__))
-        return isinstance(member, cls) and member._name_ in cls._member_map_
+                    type(obj).__qualname__, cls.__class__.__qualname__))
+        return isinstance(obj, cls) and obj._name_ in cls._member_map_
 
     def __delattr__(cls, attr):
         # nicer error message when someone tries to delete an attribute
@@ -580,7 +588,7 @@ def _get_mixins_(class_name, bases):
             return object, Enum
 
         def _find_data_type(bases):
-            data_types = []
+            data_types = set()
             for chain in bases:
                 candidate = None
                 for base in chain.__mro__:
@@ -588,19 +596,19 @@ def _find_data_type(bases):
                         continue
                     elif issubclass(base, Enum):
                         if base._member_type_ is not object:
-                            data_types.append(base._member_type_)
+                            data_types.add(base._member_type_)
                             break
                     elif '__new__' in base.__dict__:
                         if issubclass(base, Enum):
                             continue
-                        data_types.append(candidate or base)
+                        data_types.add(candidate or base)
                         break
                     else:
                         candidate = candidate or base
             if len(data_types) > 1:
                 raise TypeError('%r: too many data types: %r' % (class_name, data_types))
             elif data_types:
-                return data_types[0]
+                return data_types.pop()
             else:
                 return None
 
@@ -693,19 +701,25 @@ def __new__(cls, value):
         except Exception as e:
             exc = e
             result = None
-        if isinstance(result, cls):
-            return result
-        else:
-            ve_exc = ValueError("%r is not a valid %s" % (value, cls.__qualname__))
-            if result is None and exc is None:
-                raise ve_exc
-            elif exc is None:
-                exc = TypeError(
-                        'error in %s._missing_: returned %r instead of None or a valid member'
-                        % (cls.__name__, result)
-                        )
-            exc.__context__ = ve_exc
-            raise exc
+        try:
+            if isinstance(result, cls):
+                return result
+            else:
+                ve_exc = ValueError("%r is not a valid %s" % (value, cls.__qualname__))
+                if result is None and exc is None:
+                    raise ve_exc
+                elif exc is None:
+                    exc = TypeError(
+                            'error in %s._missing_: returned %r instead of None or a valid member'
+                            % (cls.__name__, result)
+                            )
+                if not isinstance(exc, ValueError):
+                    exc.__context__ = ve_exc
+                raise exc
+        finally:
+            # ensure all variables that could hold an exception are destroyed
+            exc = None
+            ve_exc = None
 
     def _generate_next_value_(name, start, count, last_values):
         """
diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index eb1266b..03cf353 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -11,6 +11,7 @@
 from test.support import ALWAYS_EQ, check__all__, threading_helper
 from datetime import timedelta
 
+python_version = sys.version_info[:2]
 
 # for pickle tests
 try:
@@ -347,17 +348,38 @@ class IntLogic(int, Enum):
         self.assertTrue(IntLogic.true)
         self.assertFalse(IntLogic.false)
 
-    def test_contains(self):
+    @unittest.skipIf(
+            python_version >= (3, 12),
+            '__contains__ now returns True/False for all inputs',
+            )
+    def test_contains_er(self):
         Season = self.Season
         self.assertIn(Season.AUTUMN, Season)
         with self.assertRaises(TypeError):
-            3 in Season
+            with self.assertWarns(DeprecationWarning):
+                3 in Season
         with self.assertRaises(TypeError):
-            'AUTUMN' in Season
-
+            with self.assertWarns(DeprecationWarning):
+                'AUTUMN' in Season
         val = Season(3)
         self.assertIn(val, Season)
+        #
+        class OtherEnum(Enum):
+            one = 1; two = 2
+        self.assertNotIn(OtherEnum.two, Season)
 
+    @unittest.skipIf(
+            python_version < (3, 12),
+            '__contains__ only works with enum memmbers before 3.12',
+            )
+    def test_contains_tf(self):
+        Season = self.Season
+        self.assertIn(Season.AUTUMN, Season)
+        self.assertTrue(3 in Season)
+        self.assertFalse('AUTUMN' in Season)
+        val = Season(3)
+        self.assertIn(val, Season)
+        #
         class OtherEnum(Enum):
             one = 1; two = 2
         self.assertNotIn(OtherEnum.two, Season)
@@ -1932,6 +1954,38 @@ def _missing_(cls, item):
         else:
             raise Exception('Exception not raised.')
 
+    def test_missing_exceptions_reset(self):
+        import weakref
+        #
+        class TestEnum(enum.Enum):
+            VAL1 = 'val1'
+            VAL2 = 'val2'
+        #
+        class Class1:
+            def __init__(self):
+                # Gracefully handle an exception of our own making
+                try:
+                    raise ValueError()
+                except ValueError:
+                    pass
+        #
+        class Class2:
+            def __init__(self):
+                # Gracefully handle an exception of Enum's making
+                try:
+                    TestEnum('invalid_value')
+                except ValueError:
+                    pass
+        # No strong refs here so these are free to die.
+        class_1_ref = weakref.ref(Class1())
+        class_2_ref = weakref.ref(Class2())
+        #
+        # The exception raised by Enum creates a reference loop and thus
+        # Class2 instances will stick around until the next gargage collection
+        # cycle, unlike Class1.
+        self.assertIs(class_1_ref(), None)
+        self.assertIs(class_2_ref(), None)
+
     def test_multiple_mixin(self):
         class MaxMixin:
             @classproperty
@@ -2085,7 +2139,7 @@ def test_empty_globals(self):
         exec(code, global_ns, local_ls)
 
     @unittest.skipUnless(
-            sys.version_info[:2] == (3, 9),
+            python_version == (3, 9),
             'private variables are now normal attributes',
             )
     def test_warning_for_private_variables(self):
@@ -2390,19 +2444,42 @@ def test_pickle(self):
         test_pickle_dump_load(self.assertIs, FlagStooges.CURLY|FlagStooges.MOE)
         test_pickle_dump_load(self.assertIs, FlagStooges)
 
-    def test_contains(self):
+    @unittest.skipIf(
+            python_version >= (3, 12),
+            '__contains__ now returns True/False for all inputs',
+            )
+    def test_contains_er(self):
         Open = self.Open
         Color = self.Color
         self.assertFalse(Color.BLACK in Open)
         self.assertFalse(Open.RO in Color)
         with self.assertRaises(TypeError):
-            'BLACK' in Color
+            with self.assertWarns(DeprecationWarning):
+                'BLACK' in Color
         with self.assertRaises(TypeError):
-            'RO' in Open
+            with self.assertWarns(DeprecationWarning):
+                'RO' in Open
         with self.assertRaises(TypeError):
-            1 in Color
+            with self.assertWarns(DeprecationWarning):
+                1 in Color
         with self.assertRaises(TypeError):
-            1 in Open
+            with self.assertWarns(DeprecationWarning):
+                1 in Open
+
+    @unittest.skipIf(
+            python_version < (3, 12),
+            '__contains__ only works with enum memmbers before 3.12',
+            )
+    def test_contains_tf(self):
+        Open = self.Open
+        Color = self.Color
+        self.assertFalse(Color.BLACK in Open)
+        self.assertFalse(Open.RO in Color)
+        self.assertFalse('BLACK' in Color)
+        self.assertFalse('RO' in Open)
+        self.assertTrue(1 in Color)
+        self.assertTrue(1 in Open)
+
 
     def test_member_contains(self):
         Perm = self.Perm
@@ -2883,7 +2960,11 @@ def test_programatic_function_from_empty_tuple(self):
         self.assertEqual(len(lst), len(Thing))
         self.assertEqual(len(Thing), 0, Thing)
 
-    def test_contains(self):
+    @unittest.skipIf(
+            python_version >= (3, 12),
+            '__contains__ now returns True/False for all inputs',
+            )
+    def test_contains_er(self):
         Open = self.Open
         Color = self.Color
         self.assertTrue(Color.GREEN in Color)
@@ -2891,13 +2972,33 @@ def test_contains(self):
         self.assertFalse(Color.GREEN in Open)
         self.assertFalse(Open.RW in Color)
         with self.assertRaises(TypeError):
-            'GREEN' in Color
+            with self.assertWarns(DeprecationWarning):
+                'GREEN' in Color
         with self.assertRaises(TypeError):
-            'RW' in Open
+            with self.assertWarns(DeprecationWarning):
+                'RW' in Open
         with self.assertRaises(TypeError):
-            2 in Color
+            with self.assertWarns(DeprecationWarning):
+                2 in Color
         with self.assertRaises(TypeError):
-            2 in Open
+            with self.assertWarns(DeprecationWarning):
+                2 in Open
+
+    @unittest.skipIf(
+            python_version < (3, 12),
+            '__contains__ only works with enum memmbers before 3.12',
+            )
+    def test_contains_tf(self):
+        Open = self.Open
+        Color = self.Color
+        self.assertTrue(Color.GREEN in Color)
+        self.assertTrue(Open.RW in Open)
+        self.assertTrue(Color.GREEN in Open)
+        self.assertTrue(Open.RW in Color)
+        self.assertFalse('GREEN' in Color)
+        self.assertFalse('RW' in Open)
+        self.assertTrue(2 in Color)
+        self.assertTrue(2 in Open)
 
     def test_member_contains(self):
         Perm = self.Perm
@@ -3267,7 +3368,7 @@ def test_convert(self):
                           if name[0:2] not in ('CO', '__')],
                          [], msg='Names other than CONVERT_TEST_* found.')
 
-    @unittest.skipUnless(sys.version_info[:2] == (3, 8),
+    @unittest.skipUnless(python_version == (3, 8),
                          '_convert was deprecated in 3.8')
     def test_convert_warn(self):
         with self.assertWarns(DeprecationWarning):
@@ -3276,7 +3377,7 @@ def test_convert_warn(self):
                 ('test.test_enum', '__main__')[__name__=='__main__'],
                 filter=lambda x: x.startswith('CONVERT_TEST_'))
 
-    @unittest.skipUnless(sys.version_info >= (3, 9),
+    @unittest.skipUnless(python_version >= (3, 9),
                          '_convert was removed in 3.9')
     def test_convert_raise(self):
         with self.assertRaises(AttributeError):
@@ -3285,6 +3386,33 @@ def test_convert_raise(self):
                 ('test.test_enum', '__main__')[__name__=='__main__'],
                 filter=lambda x: x.startswith('CONVERT_TEST_'))
 
+class TestHelpers(unittest.TestCase):
+
+    sunder_names = '_bad_', '_good_', '_what_ho_'
+    dunder_names = '__mal__', '__bien__', '__que_que__'
+    private_names = '_MyEnum__private', '_MyEnum__still_private'
+    private_and_sunder_names = '_MyEnum__private_', '_MyEnum__also_private_'
+    random_names = 'okay', '_semi_private', '_weird__', '_MyEnum__'
+
+    def test_sunder(self):
+        for name in self.sunder_names + self.private_and_sunder_names:
+            self.assertTrue(enum._is_sunder(name), '%r is a not sunder name?' % name)
+        for name in self.dunder_names + self.private_names + self.random_names:
+            self.assertFalse(enum._is_sunder(name), '%r is a sunder name?' % name)
+
+    def test_dunder(self):
+        for name in self.dunder_names:
+            self.assertTrue(enum._is_dunder(name), '%r is a not dunder name?' % name)
+        for name in self.sunder_names + self.private_names + self.private_and_sunder_names + self.random_names:
+            self.assertFalse(enum._is_dunder(name), '%r is a dunder name?' % name)
+
+    def test_is_private(self):
+        for name in self.private_names + self.private_and_sunder_names:
+            self.assertTrue(enum._is_private('MyEnum', name), '%r is a not private name?')
+        for name in self.sunder_names + self.dunder_names + self.random_names:
+            self.assertFalse(enum._is_private('MyEnum', name), '%r is a private name?')
+
 
 if __name__ == '__main__':
     unittest.main()
+