Logfmt Logger for Python

An opinionated logging Formatter following the Logfmt format with sane defaults.

It is production ready, fully tested, and based on the standard Python logging library.

This is base on the work of https://github.com/wlonk/logfmt-python

Usage

from logfmt_logger import getLogger

logger = getLogger("my_app")


def run():
    logger.info('Service "my_app" is running!')


if __name__ == "__main__":
    run()

Running python test.py will output this to stderr:

time=2021-03-02T17:11:04.632448 level=INFO location=test.py:7:run msg="Service is running!"

Some details about the log content:

• The time is in ISO 8601 format with milliseconds (from datetime.isoFormat)
• The level is always in uppercase letter
• the location is formated as "::"
• double quotes in strings are escaped

Setting logging level

You can set the logging level using the level option of getLogger using the standard logging levels, for example:

import logging
from logfmt_logger import getLogger

logger = getLogger("my_app", logging.ERROR)
logger.info("This won't appear...")
logger.error("This will appear!")

Log exceptions

Exception can be logged with exc_info=True:

from logfmt_logger import getLogger

logger = getLogger("my_app")

try:
    raise ValueError('Exception message with "double quotes"')
except ValueError:
    logger.info("exception", exc_info=True)

Result log line is:

time=2021-03-02T17:24:55.424014 level=INFO location=test.py:8:<module> msg="exception"  exception="Traceback (most recent call last):
  File \"test.py\", line 6, in <module>
    raise ValueError('Exception message with \"double quotes\"')
ValueError: Exception message with \"double quotes\""

Add more context

If you need to include extra data to the log line use the extra option with a context entry containing your custom key values:

from logfmt_logger import getLogger

logger = getLogger("my_app")

logger.error(
    "log context",
    extra={"context": {"test": 'this is a "with double quote" context'}},
)

Will result in:

time=2021-03-02T17:33:17.567084 level=ERROR location=test.py:5:<module> msg="log context" test="this is a \"with double quote\" context"

Contributing

The package use Poetry for its packaging. You can enter a development shell by running:

poetry install
poetry shell

The code is checked and tested with:

poetry install
poetry shell
./lint.sh # Use -f for autoformat
./test.sh