Fixed #16288 -- Enabled django.request exception logger regardless of DEBUG setting.

Thanks Matt Bennett for report and draft patch; Vinay Sajip and Russell Keith-Magee for review.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16444 bcc190cf-cafb-0310-a4f2-bffc1f526a37

docs/topics/logging.txt

@@ -501,3 +501,37 @@ Python logging module.
     :ref:`Filtering error reports<filtering-error-reports>`.
 
 .. _django-sentry: http://pypi.python.org/pypi/django-sentry
+
+
+Filters
+-------
+
+Django provides one log filter in addition to those provided by the
+Python logging module.
+
+.. class:: CallbackFilter(callback)
+
+   .. versionadded:: 1.4
+
+   This filter accepts a callback function (which should accept a single
+   argument, the record to be logged), and calls it for each record that passes
+   through the filter. Handling of that record will not proceed if the callback
+   returns False.
+
+   This filter is used as follows in the default :setting:`LOGGING`
+   configuration to ensure that the :class:`AdminEmailHandler` only sends error
+   emails to admins when :setting:`DEBUG` is `False`::
+
+       'filters': {
+            'require_debug_false': {
+                '()': 'django.utils.log.CallbackFilter',
+                'callback': lambda r: not DEBUG
+            }
+        },
+        'handlers': {
+            'mail_admins': {
+                'level': 'ERROR',
+                'filters': ['require_debug_false'],
+                'class': 'django.utils.log.AdminEmailHandler'
+            }
+        },