Removed an obsolete unicity check.

It doesn't account for app configs.

Refs #21679.

django/conf/__init__.py

@@ -104,11 +104,6 @@ def __setattr__(self, name, value):
         elif name == "ALLOWED_INCLUDE_ROOTS" and isinstance(value, six.string_types):
             raise ValueError("The ALLOWED_INCLUDE_ROOTS setting must be set "
                 "to a tuple, not a string.")
-        elif name == "INSTALLED_APPS":
-            value = list(value)  # force evaluation of generators on Python 3
-            if len(value) != len(set(value)):
-                raise ImproperlyConfigured("The INSTALLED_APPS setting must contain unique values.")
-
         object.__setattr__(self, name, value)
 
 

tests/settings_tests/tests.py

@@ -292,27 +292,6 @@ def test_complex_override_warning(self):
                 'Overriding setting TEST_WARN can lead to unexpected behaviour.')
 
 
-class UniqueSettingsTests(TestCase):
-    """
-    Tests for the INSTALLED_APPS setting.
-    """
-    settings_module = settings
-
-    def setUp(self):
-        self._installed_apps = self.settings_module.INSTALLED_APPS
-
-    def tearDown(self):
-        self.settings_module.INSTALLED_APPS = self._installed_apps
-
-    def test_unique(self):
-        """
-        An ImproperlyConfigured exception is raised if the INSTALLED_APPS contains
-        any duplicate strings.
-        """
-        with self.assertRaises(ImproperlyConfigured):
-            self.settings_module.INSTALLED_APPS = ("myApp1", "myApp1", "myApp2", "myApp3")
-
-
 class TrailingSlashURLTests(TestCase):
     """
     Tests for the MEDIA_URL and STATIC_URL settings.