I would like to understand if it's possible and how is it possible, to modify the message part of a log message, using the Python logging module.
So basically, you can format a complete log as:
format = '{"timestamp": "%(asctime)s", "logger_level": "%(levelname)s", "log_message": %(message)s}'
However, I would like to make sure the message part is always in json format. Is there any way I can modify the format of only the message part, maybe with a custom logging.Formatter?
Thank you.
The format specification %(message)s tells Python you want to format a string. Try it with %(message)r and it should do the job:
>>> logging.error('{"log_message": %r}', {"a": 55})
ERROR:root:{"log_message": {'a': 55}}
There's an example in the Logging Cookbook which shows one way of doing this.Basically:
import json
import logging
class StructuredMessage:
def __init__(self, message, /, **kwargs):
self.message = message
self.kwargs = kwargs
def __str__(self):
return '%s >>> %s' % (self.message, json.dumps(self.kwargs))
_ = StructuredMessage # optional, to improve readability
logging.basicConfig(level=logging.INFO, format='%(message)s')
logging.info(_('message 1', foo='bar', bar='baz', num=123, fnum=123.456))
Of course, you can adapt this basic idea to do something closer to what you want/need.
Update: The formatting only happens if the message is actually output. Also, it won't apply to logging from third-party libraries. You would need to subclass Logger before importing any other modules which import logging to achieve that, but it's a documented approach.
log["log_message"]to be a dictionary, instead of a string? (After parsing the log string as json, of course.)