contextlogger 0.0.3

A logging boilerplate enhanced by the use of contextvars

Context Logger

A simple logger that uses the contexvars library to inject extra details in your logs.

Installation

pip install contextlogger

Usage

This should be as simple as it gets!

Let's assume that we have a package with the following structure:

- my_app
  - my_app
    - __init__.py
    - runner.py
  main.py

where your main.py is simply running the two tasks defined in your runner.py module.

""" main.py """
import asyncio

from my_app.runner import task1, task2


async def main():
	await asyncio.gather(
		task1(),
		task2(),
	)
asyncio.run(main())

""" runner.py """
async def task1():
	pass

async def task2():
	pass

In the __init__.py module of your project setup your logger as you would normaly do. (you might want to skip logging to a file)

""" __init__.py """
import logging
from logging.handlers import TimedRotatingFileHandler
import os

import contextlogger

# Create a CLogger instance
clogger = contextlogger.getCLogger(__name__)

# Create a logging formatter
logging_format = "%(asctime)s %(levelname)s %(name)s %(message)s"
formatter = logging.Formatter(logging_format)

# Create handlers for console logger
console_handler = logging.StreamHandler()
console_handler.setFormatter(formatter)
clogger.addHandler(console_handler)

# Create handlers for file logger
LOG_DIR = 'logs'
APP = 'MY-APP'
if not os.path.exists(LOG_DIR):
	os.makedirs(LOG_DIR)

file_handler = TimedRotatingFileHandler(f"{LOG_DIR}/{APP}.log", when="midnight", interval=1)
file_handler.setFormatter(formatter)
file_handler.suffix = "%Y%m%d"
clogger.addHandler(file_handler)

Notice that instead of using the getLogger function of the standard logging library, we now use the getCLogger from the contextlogger package.

Once your logger configuration is set, you can use your logger in your runner.py file (or whichever the entry point of your package you chose to be)

""" runner.py """
from my_app import clogger

async def task1():
	clogger.info(f"Hello from {task1.__name__}")

async def task2():
	clogger.info(f"Hello from {task2.__name__}")

As expected, the output of the clogger will be:

2020-12-06 18:07:27,008 INFO my_app Hello from task1
2020-12-06 18:07:27,009 INFO my_app Hello from task2

Now lets add some context to our logging.

We can do that by adding a list of CLogVar (context log variables) to our logger.

Let's add a 'static' attribute... Not very useful but why not!

""" runner.py """
from contextlogger import CLogVar
from my_app import clogger

clogger.clogvars = [
	CLogVar(name='static'),
]

async def task1():
    # Set our 'static' value for task1
	clogger.setvar('static', value=1)

	clogger.info(f"Hello from {task1.__name__}")

async def task2():
    # Set our 'static' value for task2
	clogger.setvar('static', value=2)

	clogger.info(f"Hello from {task2.__name__}")

And voila! Now the output of the clogger includes our static values:

2020-12-06 18:12:07,505 INFO my_app {'static': 1} Hello from task1
2020-12-06 18:12:07,505 INFO my_app {'static': 2} Hello from task2

Ok but that was not very handy, right? Let's do something more realistic. Let's pretend that this is our FastApi application and we want to add a 'request_id' to every request we receive.

Now, things get interesting! Our CLogVar can also accept a 'setter' argument which is a function that generates a new uuid every time we enter a new context. Every time we call the setvar without a value, it will try to find a setter to do the job!

from uuid import uuid4

from contextlogger import CLogVar
from my_app import clogger

clogger.clogvars = [
	CLogVar(name='static'),
	CLogVar(name='request_id', setter=lambda: str(uuid4())),
]

async def task1():
	# Set our 'static' value for task1
	clogger.setvar('static', value=1)

	# Set our request_id value for task1
	clogger.setvar('request_id')

	clogger.info(f"Hello from {task1.__name__}")

async def task2():
    # Set our 'static' value for task2
	clogger.setvar('static', value=2)

	# Set our 'request_id' value for task2
	clogger.setvar('request_id')

	clogger.info(f"Hello from {task2.__name__}")

And here we are, with something a lot more useful than just a static value:

2020-12-06 18:21:17,626 INFO my_app {'request_id': 'd3961bd9-f701-4222-ad32-f204e9eb968a', 'static': 1} Hello from task1
2020-12-06 18:21:17,626 INFO my_app {'request_id': '6d4cdab2-e24b-481b-b54b-12c6ee9bcc1b', 'static': 2} Hello from task2

Finally, let's add an extra module just for sake of it.

Now our directory will look like:

- my_app
  - my_app
    - __init__.py
    - runner.py
    - another_module.py
  main.py

where our another_module.py simply imports the logger and uses it in a function:

from my_app import clogger


def test():
	clogger.info(f"Hello from another_module")

Now, if we call our test function inside the task1 of our runner.py:

from uuid import uuid4

from contextlogger import CLogVar
from my_app import clogger
from my_app.another_module import test

clogger.clogvars = [
	CLogVar(name='static'),
	CLogVar(name='request_id', setter=lambda: str(uuid4())),
]

async def task1():
	# Set our 'static' value for task1
	clogger.setvar('static', value=1)

	# Set our request_id value for task1
	clogger.setvar('request_id')

	clogger.info(f"Hello from {task1.__name__}")

	test()

async def task2():
    # Set our 'static' value for task2
	clogger.setvar('static', value=2)

	# Set our 'request_id' value for task2
	clogger.setvar('request_id')

	clogger.info(f"Hello from {task2.__name__}")

we should see that the log line that is printed inside our another_module.py has the same uuid with the log line that is printed in task1

2020-12-06 18:33:36,634 INFO my_app {'request_id': '1eff5e40-4b05-4cd1-bd9c-edbee85d2995', 'static': 1} Hello from task1
2020-12-06 18:33:36,635 INFO my_app {'request_id': '1eff5e40-4b05-4cd1-bd9c-edbee85d2995', 'static': 1} Hello from another_module
2020-12-06 18:33:36,635 INFO my_app {'request_id': 'ec68779f-46f6-4ea0-a003-9ddb053887e1', 'static': 2} Hello from task2

Contribute

I am currently working on the contributions documentation so for now, if you would like to create a pull request drop me a message on instagram.

Authors

Christos Liontos