Fixed #28810 -- Replaced '%' style logging formatting with str.format() style.

django/utils/log.py

@@ -27,7 +27,8 @@ DEFAULT_LOGGING = {
     'formatters': {
         'django.server': {
             '()': 'django.utils.log.ServerFormatter',
-            'format': '[%(server_time)s] %(message)s',
+            'format': '[{server_time}] {message}',
+            'style': '{',
         }
     },
     'handlers': {
@@ -190,4 +191,4 @@ class ServerFormatter(logging.Formatter):
         return super().format(record)
 
     def uses_server_time(self):
-        return self._fmt.find('%(server_time)') >= 0
+        return self._fmt.find('{server_time}') >= 0

docs/topics/logging.txt

@@ -299,10 +299,12 @@ Finally, here's an example of a fairly complex logging setup::
         'disable_existing_loggers': False,
         'formatters': {
             'verbose': {
-                'format': '%(levelname)s %(asctime)s %(module)s %(process)d %(thread)d %(message)s'
+                'format': '{levelname} {asctime} {module} {process:d} {thread:d} {message}',
+                'style': '{',
             },
             'simple': {
-                'format': '%(levelname)s %(message)s'
+                'format': '{levelname} {message}',
+                'style': '{',
             },
         },
         'filters': {