Fixed #18824 -- Allow deleting a setting from overriden settings

django/conf/__init__.py

@@ -152,11 +152,22 @@ class UserSettingsHolder(BaseSettings):
         Requests for configuration variables not in this class are satisfied
         from the module specified in default_settings (if possible).
         """
+        self.__dict__['_deleted'] = set()
         self.default_settings = default_settings
 
     def __getattr__(self, name):
+        if name in self._deleted:
+            raise AttributeError
         return getattr(self.default_settings, name)
 
+    def __setattr__(self, name, value):
+        self._deleted.discard(name)
+        return super(UserSettingsHolder, self).__setattr__(name, value)
+
+    def __delattr__(self, name):
+        self._deleted.add(name)
+        return super(UserSettingsHolder, self).__delattr__(name)
+
     def __dir__(self):
         return list(self.__dict__) + dir(self.default_settings)
 

tests/regressiontests/settings_tests/tests.py

@@ -148,6 +148,16 @@ class SettingsTests(TestCase):
     def test_settings_delete_wrapped(self):
         self.assertRaises(TypeError, delattr, settings, '_wrapped')
 
+    def test_override_settings_delete(self):
+        """
+        Allow deletion of a setting in an overriden settings set (#18824)
+        """
+        previous_i18n = settings.USE_I18N
+        with self.settings(USE_I18N=False):
+            del settings.USE_I18N
+            self.assertRaises(AttributeError, getattr, settings, 'USE_I18N')
+        self.assertEqual(settings.USE_I18N, previous_i18n)
+
     def test_allowed_include_roots_string(self):
         """
         ALLOWED_INCLUDE_ROOTS is not allowed to be incorrectly set to a string