logging: Make our own Formatter class.

This doesn't yet do much, but it gives us a suitable place to
add code to customize how log messages are displayed, beyond what
a format string passed to the default formatter can do.

tools/linter_lib/custom_check.py

@@ -204,8 +204,6 @@ def build_custom_checkers(by_lang):
          'exclude_line': set([
              ('zerver/views/users.py',
               "return json_error(_(\"Email '%(email)s' not allowed for realm '%(realm)s'\") %"),
-             ('zproject/settings.py',
-              "'format': '%(asctime)s %(levelname)-8s %(message)s'"),
              ('static/templates/settings/bot-settings.handlebars',
               "'https://hostname.example.com/bots/followup'"),
          ]),

zerver/lib/logging_util.py

@@ -125,6 +125,17 @@ def skip_site_packages_logs(record):
         return False
     return True
 
+class ZulipFormatter(logging.Formatter):
+    _fmt = '%(asctime)s %(levelname)-8s %(message)s'
+
+    def __init__(self):
+        # type: () -> None
+        super().__init__(fmt=self._fmt)
+
+    def format(self, record):
+        # type: (logging.LogRecord) -> str
+        return super().format(record)
+
 def create_logger(name, log_file, log_level, log_format="%(asctime)s %(levelname)-8s %(message)s"):
     # type: (str, str, str, str) -> Logger
     """Creates a named logger for use in logging content to a certain

zproject/settings.py

@@ -1051,7 +1051,7 @@ LOGGING = {
     'disable_existing_loggers': False,
     'formatters': {
         'default': {
-            'format': '%(asctime)s %(levelname)-8s %(message)s'
+            '()': 'zerver.lib.logging_util.ZulipFormatter',
         }
     },
     'filters': {