diff --git a/Lib/enum.py b/Lib/enum.py
index bcf411c..bccf024 100644
--- a/Lib/enum.py
+++ b/Lib/enum.py
@@ -280,7 +280,8 @@ def __set_name__(self, enum_class, member_name):
             # linear.
             enum_class._value2member_map_.setdefault(value, enum_member)
         except TypeError:
-            pass
+            # keep track of the value in a list so containment checks are quick
+            enum_class._unhashable_values_.append(value)
 
 
 class _EnumDict(dict):
@@ -440,6 +441,7 @@ def __new__(metacls, cls, bases, classdict, *, boundary=None, _simple=False, **k
         classdict['_member_names_'] = []
         classdict['_member_map_'] = {}
         classdict['_value2member_map_'] = {}
+        classdict['_unhashable_values_'] = []
         classdict['_member_type_'] = member_type
         #
         # Flag structures (will be removed if final class is not a Flag
@@ -622,6 +624,13 @@ def __call__(cls, value, names=None, *, module=None, qualname=None, type=None, s
 
     def __contains__(cls, member):
         if not isinstance(member, Enum):
+            import warnings
+            warnings.warn(
+                    "in 3.12 __contains__ will no longer raise TypeError, but will return True or\n"
+                    "False depending on whether the value is a member or the value of a member",
+                    DeprecationWarning,
+                    stacklevel=2,
+                    )
             raise TypeError(
                 "unsupported operand type(s) for 'in': '%s' and '%s'" % (
                     type(member).__qualname__, cls.__class__.__qualname__))
@@ -1005,14 +1014,15 @@ def __format__(self, format_spec):
             val = str(self)
         # mix-in branch
         else:
-            import warnings
-            warnings.warn(
-                    "in 3.12 format() will use the enum member, not the enum member's value;\n"
-                    "use a format specifier, such as :d for an IntEnum member, to maintain"
-                    "the current display",
-                    DeprecationWarning,
-                    stacklevel=2,
-                    )
+            if not format_spec or format_spec in ('{}','{:}'):
+                import warnings
+                warnings.warn(
+                        "in 3.12 format() will use the enum member, not the enum member's value;\n"
+                        "use a format specifier, such as :d for an IntEnum member, to maintain"
+                        "the current display",
+                        DeprecationWarning,
+                        stacklevel=2,
+                        )
             cls = self._member_type_
             val = self._value_
         return cls.__format__(val, format_spec)
@@ -1434,6 +1444,7 @@ def convert_class(cls):
         body['_member_names_'] = member_names = []
         body['_member_map_'] = member_map = {}
         body['_value2member_map_'] = value2member_map = {}
+        body['_unhashable_values_'] = []
         body['_member_type_'] = member_type = etype._member_type_
         if issubclass(etype, Flag):
             body['_boundary_'] = boundary or etype._boundary_
diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index 983c54b..e918b03 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -16,6 +16,8 @@
 from test.support import threading_helper
 from datetime import timedelta
 
+python_version = sys.version_info[:2]
+
 def load_tests(loader, tests, ignore):
     tests.addTests(doctest.DocTestSuite(enum))
     if os.path.exists('Doc/library/enum.rst'):
@@ -352,17 +354,38 @@ 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)
@@ -528,8 +551,16 @@ def __format__(self, spec):
         self.assertEqual(str(TestFloat.one), 'one')
         self.assertEqual('{}'.format(TestFloat.one), 'TestFloat success!')
 
-    @unittest.skipUnless(
-            sys.version_info[:2] < (3, 12),
+    @unittest.skipIf(
+            python_version < (3, 12),
+            'mixin-format is still using member.value',
+            )
+    def test_mixin_format_warning(self):
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(f'{self.Grades.B}', 'Grades.B')
+
+    @unittest.skipIf(
+            python_version >= (3, 12),
             'mixin-format now uses member instead of member.value',
             )
     def test_mixin_format_warning(self):
@@ -537,7 +568,11 @@ def test_mixin_format_warning(self):
             self.assertEqual(f'{self.Grades.B}', '4')
 
     def assertFormatIsValue(self, spec, member):
-        self.assertEqual(spec.format(member), spec.format(member.value))
+        if python_version < (3, 12) and (not spec or spec in ('{}','{:}')):
+            with self.assertWarns(DeprecationWarning):
+                self.assertEqual(spec.format(member), spec.format(member.value))
+        else:
+            self.assertEqual(spec.format(member), spec.format(member.value))
 
     def test_format_enum_date(self):
         Holiday = self.Holiday
@@ -2202,7 +2237,7 @@ def __repr__(self):
                 description   = 'Bn$',      3
 
     @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):
@@ -2225,7 +2260,7 @@ class Private(Enum):
         self.assertEqual(Private._Private__major_, 'Hoolihan')
 
     @unittest.skipUnless(
-            sys.version_info[:2] < (3, 12),
+            python_version < (3, 12),
             'member-member access now raises an exception',
             )
     def test_warning_for_member_from_member_access(self):
@@ -2237,7 +2272,7 @@ class Di(Enum):
         self.assertIs(Di.NO, nope)
 
     @unittest.skipUnless(
-            sys.version_info[:2] >= (3, 12),
+            python_version >= (3, 12),
             'member-member access currently issues a warning',
             )
     def test_exception_for_member_from_member_access(self):
@@ -2617,19 +2652,41 @@ 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
@@ -2954,10 +3011,15 @@ def test_repr(self):
         self.assertEqual(repr(~(Open.WO | Open.CE)), 'Open.RW')
         self.assertEqual(repr(Open(~4)), '-5')
 
+    @unittest.skipUnless(
+            python_version < (3, 12),
+            'mixin-format now uses member instead of member.value',
+            )
     def test_format(self):
-        Perm = self.Perm
-        self.assertEqual(format(Perm.R, ''), '4')
-        self.assertEqual(format(Perm.R | Perm.X, ''), '5')
+        with self.assertWarns(DeprecationWarning):
+            Perm = self.Perm
+            self.assertEqual(format(Perm.R, ''), '4')
+            self.assertEqual(format(Perm.R | Perm.X, ''), '5')
 
     def test_or(self):
         Perm = self.Perm
@@ -3189,7 +3251,11 @@ 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)
@@ -3197,13 +3263,33 @@ 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
@@ -3685,7 +3771,7 @@ 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):
@@ -3694,7 +3780,7 @@ 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):
@@ -3703,6 +3789,10 @@ def test_convert_raise(self):
                 ('test.test_enum', '__main__')[__name__=='__main__'],
                 filter=lambda x: x.startswith('CONVERT_TEST_'))
 
+    @unittest.skipUnless(
+            python_version < (3, 12),
+            'mixin-format now uses member instead of member.value',
+            )
     def test_convert_repr_and_str(self):
         module = ('test.test_enum', '__main__')[__name__=='__main__']
         test_type = enum.IntEnum._convert_(
@@ -3711,7 +3801,8 @@ def test_convert_repr_and_str(self):
                 filter=lambda x: x.startswith('CONVERT_STRING_TEST_'))
         self.assertEqual(repr(test_type.CONVERT_STRING_TEST_NAME_A), '%s.CONVERT_STRING_TEST_NAME_A' % module)
         self.assertEqual(str(test_type.CONVERT_STRING_TEST_NAME_A), 'CONVERT_STRING_TEST_NAME_A')
-        self.assertEqual(format(test_type.CONVERT_STRING_TEST_NAME_A), '5')
+        with self.assertWarns(DeprecationWarning):
+            self.assertEqual(format(test_type.CONVERT_STRING_TEST_NAME_A), '5')
 
 # global names for StrEnum._convert_ test
 CONVERT_STR_TEST_2 = 'goodbye'
diff --git a/Lib/test/test_signal.py b/Lib/test/test_signal.py
index 06b644e..daecf19 100644
--- a/Lib/test/test_signal.py
+++ b/Lib/test/test_signal.py
@@ -1323,7 +1323,7 @@ def cycle_handlers():
                     # race condition, check it.
                     self.assertIsInstance(cm.unraisable.exc_value, OSError)
                     self.assertIn(
-                        f"Signal {signum} ignored due to race condition",
+                        f"Signal {signum:d} ignored due to race condition",
                         str(cm.unraisable.exc_value))
                     ignored = True