python - Django logging custom attributes in formatter

Question

How can Django use logging to log using custom attributes in the formatter? I'm thinking of logging the logged in username for example.

In the settings.py script, the LOGGING variable is defined:

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'filters': {
        'require_debug_false': {
            '()': 'django.utils.log.RequireDebugFalse'
        },
    },
    'formatters' : {
        'info_format' : {
            'format' : '%(asctime)s %(levelname)s - %(message)s',
        },
    }
}

I wish to use a format, something like:

'format' : '%(asctime).19s %(levelname)s - %(username)s: %(message)s'

Where username would be the currently logged in user. Maybe any other kind of session's variables may be added here.

A workaround here is to use the extra parameter on the logger methods, which receives a dictionary with the keys as the strings I want to use on the format string:

logger.info(message, extra={'username' : request.user.username})

Another (ugly) workaround would be to build the message attribute to include the things that are not part of the default attributes that logging formatters have.

message = request.user.username + " - " + message
logger.info(message)

But, is there a way to set up the format string with certain attributes and make Django give them automatically to the logging API? If %(username)s for example, the request.user.username, of any others perhaps...

Answer 1

You can use a filter to add your custom attribute. For example :

def add_my_custom_attribute(record):
    record.myAttribute = 'myValue'
    record.username = record.request.user.username 
    return True

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'filters': {
        ...
        'add_my_custom_attribute': {
            '()': 'django.utils.log.CallbackFilter',
            'callback': add_my_custom_attribute,
        }
    },
    'handlers': {
        ...
        'django.server': {
            'level': 'INFO',
            'class': 'logging.StreamHandler',
            'filters': ['add_my_custom_attribute'],
            'formatter': 'django.server',
        },            
    },
    ...
}

---

By installing a filter, you can process each log record and decide whether it should be passed from logger to handler.

The filter get the log record which contains all the details of log (i.e : time, severity, request, status code).

The attributes of the record are used by the formatter to format it to string message. If you add your custom attributes to that record - they will also be available to the formatter.