Fixed #14861 -- Moved logging config outside of Settings.__init__

Thanks donspaulding for the report and simonpercivall for the
initial patch.

django/conf/__init__.py

@@ -43,13 +43,28 @@ class LazySettings(LazyObject):
                 % (name, ENVIRONMENT_VARIABLE))
 
         self._wrapped = Settings(settings_module)
-
+        self._configure_logging()
 
     def __getattr__(self, name):
         if self._wrapped is empty:
             self._setup(name)
         return getattr(self._wrapped, name)
 
+    def _configure_logging(self):
+        """
+        Setup logging from LOGGING_CONFIG and LOGGING settings.
+        """
+        if self.LOGGING_CONFIG:
+            # First find the logging configuration function ...
+            logging_config_path, logging_config_func_name = self.LOGGING_CONFIG.rsplit('.', 1)
+            logging_config_module = importlib.import_module(logging_config_path)
+            logging_config_func = getattr(logging_config_module, logging_config_func_name)
+
+            # Backwards-compatibility shim for #16288 fix
+            compat_patch_logging_config(self.LOGGING)
+
+            # ... then invoke it with the logging settings
+            logging_config_func(self.LOGGING)
 
     def configure(self, default_settings=global_settings, **options):
         """
@@ -133,19 +148,6 @@ class Settings(BaseSettings):
             os.environ['TZ'] = self.TIME_ZONE
             time.tzset()
 
-        # Settings are configured, so we can set up the logger if required
-        if self.LOGGING_CONFIG:
-            # First find the logging configuration function ...
-            logging_config_path, logging_config_func_name = self.LOGGING_CONFIG.rsplit('.', 1)
-            logging_config_module = importlib.import_module(logging_config_path)
-            logging_config_func = getattr(logging_config_module, logging_config_func_name)
-
-            # Backwards-compatibility shim for #16288 fix
-            compat_patch_logging_config(self.LOGGING)
-
-            # ... then invoke it with the logging settings
-            logging_config_func(self.LOGGING)
-
 
 class UserSettingsHolder(BaseSettings):
     """

docs/topics/logging.txt

@@ -345,36 +345,6 @@ This logging configuration does the following things:
     printed to the console; ``ERROR`` and ``CRITICAL``
     messages will also be output via email.
 
-.. admonition:: Custom handlers and circular imports
-
-    If your ``settings.py`` specifies a custom handler class and the file
-    defining that class also imports ``settings.py`` a circular import will
-    occur.
-
-    For example, if ``settings.py`` contains the following config for
-    :setting:`LOGGING`::
-
-        LOGGING = {
-          'version': 1,
-          'handlers': {
-            'custom_handler': {
-              'level': 'INFO',
-              'class': 'myproject.logconfig.MyHandler',
-            }
-          }
-        }
-
-    and ``myproject/logconfig.py`` has the following line before the
-    ``MyHandler`` definition::
-
-        from django.conf import settings
-
-    then the ``dictconfig`` module will raise an exception like the following::
-
-        ValueError: Unable to configure handler 'custom_handler':
-        Unable to configure handler 'custom_handler':
-        'module' object has no attribute 'logconfig'
-
 .. _formatter documentation: http://docs.python.org/library/logging.html#formatter-objects
 
 Custom logging configuration

tests/regressiontests/logging_tests/logconfig.py

+import logging
+
+from django.conf import settings
+
+class MyHandler(logging.Handler):
+    def __init__(self, *args, **kwargs):
+        self.config = settings.LOGGING

tests/regressiontests/logging_tests/tests.py

@@ -10,6 +10,8 @@ from django.test import TestCase, RequestFactory
 from django.test.utils import override_settings
 from django.utils.log import CallbackFilter, RequireDebugFalse
 
+from ..admin_scripts.tests import AdminScriptTestCase
+
 
 # logging config prior to using filter with mail_admins
 OLD_LOGGING = {
@@ -253,3 +255,30 @@ class AdminEmailHandlerTest(TestCase):
 
         self.assertEqual(len(mail.outbox), 1)
         self.assertEqual(mail.outbox[0].subject, expected_subject)
+
+
+class SettingsConfigTest(AdminScriptTestCase):
+    """
+    Test that accessing settings in a custom logging handler does not trigger
+    a circular import error.
+    """
+    def setUp(self):
+        log_config = """{
+    'version': 1,
+    'handlers': {
+        'custom_handler': {
+            'level': 'INFO',
+            'class': 'logging_tests.logconfig.MyHandler',
+        }
+    }
+}"""
+        self.write_settings('settings.py', sdict={'LOGGING': log_config})
+
+    def tearDown(self):
+        self.remove_settings('settings.py')
+
+    def test_circular_dependency(self):
+        # validate is just an example command to trigger settings configuration
+        out, err = self.run_manage(['validate'])
+        self.assertNoOutput(err)
+        self.assertOutput(out, "0 errors found")