pythongh-112451: Prohibit subclassing of datetime.timezone.

Lib/_pydatetime.py

@@ -2348,16 +2348,7 @@ def __new__(cls, offset, name=_Omitted):
         return cls._create(offset, name)
 
     def __init_subclass__(cls):
-        # When deprecation ends replace with:
-        #   raise TypeError("type 'datetime.timezone' is not an acceptable base type")
-        import warnings
-        warnings.warn(
-            "Subclassing 'datetime.timezone' is deprecated and scheduled for removal "
-            "in Python 3.15.",
-            DeprecationWarning,
-            stacklevel=2,
-        )
-        super().__init_subclass__()
+        raise TypeError("type 'datetime.timezone' is not an acceptable base type")
 
     @classmethod
     def _create(cls, offset, name=None):

Lib/test/datetimetester.py

@@ -301,21 +301,7 @@ def test_inheritance(self):
         self.assertIsInstance(timezone.utc, tzinfo)
         self.assertIsInstance(self.EST, tzinfo)
 
-    def test_cannot_subclass_deprecation_warning(self):
-        if '_Fast' in self.__class__.__name__:
-            self.skipTest('Only run for Pure Python implementation')
-
-        msg = (
-            "Subclassing 'datetime.timezone' is deprecated and scheduled for removal "
-            "in Python 3.15."
-        )
-        with self.assertWarnsRegex(DeprecationWarning, msg):
-            class MyTimezone(timezone): pass
-
     def test_cannot_subclass(self):
-        if '_Pure' in self.__class__.__name__:
-            self.skipTest('Only run for Fast C implementation')
-
         msg = "type 'datetime.timezone' is not an acceptable base type"
         with self.assertRaisesRegex(TypeError, msg):
             class MyTimezone(timezone): pass

Misc/NEWS.d/next/Library/2024-01-24-20-11-46.gh-issue-112451.7YrG4p.rst

@@ -0,0 +1,2 @@
+Prohibit subclassing pure-Python ``datetime.timezone``. This is consistent
+with C-extension implementation. Patch by Mariusz Felisiak.