How to add extra log context with loguru
Loguru is a Python library that provides a neat logging API, and I recently learned how to add extra context to the logs.
This is really nice when you’re using structured logs, because you can do all sorts of things based on the data you collect like this.
There are mainly two options:
1) Use logger.bind(**kwargs) to create a local logger with the context information
Example:
from loguru import logger
def some_func1():
ctx_logger = logger.bind(func_name='some_func1')
ctx_logger.info('Hello there!')
def some_func2():
ctx_logger = logger.bind(func_name='some_func2')
ctx_logger.info('Hiya!')
ctx_logger.info('Nice to see you here!')
# for testing, let's add an extra handler that displays the extra context:
import sys
logger.add(sys.stderr, format="{message} | {extra}")
some_func1()
some_func2()
some_func1()
Running the above example, you will see:
2023-11-07 20:06:37.883 | INFO | __main__:some_func1:3 - Hello there!
Hello there! | {'func_name': 'some_func1'}
>>> some_func2()
2023-11-07 20:06:37.883 | INFO | __main__:some_func2:3 - Hiya!
Hiya! | {'func_name': 'some_func2'}
2023-11-07 20:06:37.883 | INFO | __main__:some_func2:4 - Nice to see you here!
Nice to see you here! | {'func_name': 'some_func2'}
>>> some_func1()
2023-11-07 20:06:37.884 | INFO | __main__:some_func1:3 - Hello there!
Hello there! | {'func_name': 'some_func1'}
In the above output, we see each line logged in double: the first time by the default handler/formatter, the second one by the custom one we added which prints the extra context.
2) Use logger.contextualize(**kwargs) to add information to the context-local state
By context-local state here, I mean in the sense of a context variable, which will be the equivalent of a using a thread-local variable or an async-context-local in the case of asynchronous code.
This is useful in a web application (Django, FastAPI, etc) to add information to the logs in the context of a request being handled.
It’s as easy as:
from loguru import logger
def some_func1():
logger.info('Hello there!')
def some_func2():
logger.info('Hiya!')
logger.info('Nice to see you here!')
# for testing, let's add an extra handler that displays the extra context:
import sys
logger.add(sys.stderr, format="{message} | {extra}")
with logger.contextualize(task_id=1234):
some_func1()
some_func2()
The output for the above example will be:
2023-11-07 20:06:24.980 | INFO | __main__:some_func1:2 - Hello there!
Hello there! | {'task_id': 1234}
2023-11-07 20:06:24.980 | INFO | __main__:some_func2:2 - Hiya!
Hiya! | {'task_id': 1234}
2023-11-07 20:06:24.981 | INFO | __main__:some_func2:3 - Nice to see you here!
Nice to see you here! | {'task_id': 1234}