How to implement json format logs in python

Question

I have a below piece of code for python logging and would want to convert the logs into json format for better accessibility of information. How can I convert them into JSON format?

import os
import logging

log_fmt = ("%(asctime)-s %(levelname)-s %(message)s")

logger = logging.getLogger()
logger.setLevel(os.environ.get('LOG_LEVEL', 'INFO'))

logger.info(f"this is a test")

And the output looks like "2022-04-20 17:40:31,332 INFO this is a test"

How can I format this into a json object so I can access by keys? Desired output:

{
 "time": "2022-04-20 17:40:31,332",
 "level": "INFO",
 "message": "this is a test"
}

Answer 1

You could use the Python JSON Logger

But if you don't want to, or can't do that, then your log format string should be...

log_fmt = ("{\"time\": %(asctime)-s, \"level\": %(levelname)-s, \"message\": %(message)s},")

You'll end up with an extra comma at the end of the log file that you can programatically remove later. Or, you can do this if you want the comma at the top of the file...

log_fmt = (",{\"time\": %(asctime)-s, \"level\": %(levelname)-s, \"message\": %(message)s}")

But the json will look better in an editor with the comma at the end of every line.

If you provide a mechanism for users to download, or otherwise access log files, then you can do the trailing comma cleanup there, before you send the log file to the user.