Configure uvicorn logs with loguru for FastAPI

logger.py

"""
WARNING: dont use loguru, use structlog
https://gist.github.com/nkhitrov/38adbb314f0d35371eba4ffb8f27078f


Configure handlers and formats for application loggers.
"""
import logging
import sys
from pprint import pformat

# if you dont like imports of private modules
# you can move it to typing.py module
from loguru import logger
from loguru._defaults import LOGURU_FORMAT


class InterceptHandler(logging.Handler):
    """
    Default handler from examples in loguru documentaion.
    See https://loguru.readthedocs.io/en/stable/overview.html#entirely-compatible-with-standard-logging
    """

    def emit(self, record: logging.LogRecord):
        # Get corresponding Loguru level if it exists
        try:
            level = logger.level(record.levelname).name
        except ValueError:
            level = record.levelno

        # Find caller from where originated the logged message
        frame, depth = logging.currentframe(), 2
        while frame.f_code.co_filename == logging.__file__:
            frame = frame.f_back
            depth += 1

        logger.opt(depth=depth, exception=record.exc_info).log(
            level, record.getMessage()
        )


def format_record(record: dict) -> str:
    """
    Custom format for loguru loggers.
    Uses pformat for log any data like request/response body during debug.
    Works with logging if loguru handler it.

    Example:
    >>> payload = [{"users":[{"name": "Nick", "age": 87, "is_active": True}, {"name": "Alex", "age": 27, "is_active": True}], "count": 2}]
    >>> logger.bind(payload=).debug("users payload")
    >>> [   {   'count': 2,
    >>>         'users': [   {'age': 87, 'is_active': True, 'name': 'Nick'},
    >>>                      {'age': 27, 'is_active': True, 'name': 'Alex'}]}]
    """

    format_string = LOGURU_FORMAT
    if record["extra"].get("payload") is not None:
        record["extra"]["payload"] = pformat(
            record["extra"]["payload"], indent=4, compact=True, width=88
        )
        format_string += "\n<level>{extra[payload]}</level>"

    format_string += "{exception}\n"
    return format_string


def init_logging():
    """
    Replaces logging handlers with a handler for using the custom handler.
        
    WARNING!
    if you call the init_logging in startup event function, 
    then the first logs before the application start will be in the old format

    >>> app.add_event_handler("startup", init_logging)
    stdout:
    INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
    INFO:     Started reloader process [11528] using statreload
    INFO:     Started server process [6036]
    INFO:     Waiting for application startup.
    2020-07-25 02:19:21.357 | INFO     | uvicorn.lifespan.on:startup:34 - Application startup complete.
    
    """

    # disable handlers for specific uvicorn loggers
    # to redirect their output to the default uvicorn logger
    # works with uvicorn==0.11.6
    loggers = (
        logging.getLogger(name)
        for name in logging.root.manager.loggerDict
        if name.startswith("uvicorn.")
    )
    for uvicorn_logger in loggers:
        uvicorn_logger.handlers = []

    # change handler for default uvicorn logger
    intercept_handler = InterceptHandler()
    logging.getLogger("uvicorn").handlers = [intercept_handler]

    # set logs output, level and format
    logger.configure(
        handlers=[{"sink": sys.stdout, "level": logging.DEBUG, "format": format_record}]
    )

main.py

"""
WARNING: dont use loguru, use structlog
https://gist.github.com/nkhitrov/38adbb314f0d35371eba4ffb8f27078f

Gist for original issue https://github.com/tiangolo/fastapi/issues/1276#issuecomment-663748916
"""

from fastapi import FastAPI
from starlette.requests import Request
from logger import init_logging

app = FastAPI(title="Test Uvicorn Handlers")

init_logging()

# view.py
@app.get("/")
def index(request: Request) -> None:
    logger.info("loguru info log")
    logging.info("logging info log")

    logging.getLogger("fastapi").debug("fatapi info log")
    logger.bind(payload=dict(request.query_params)).debug("params with formating")
    return None

perfect solution! 💯 🚀

FWIW with uvicorn==0.18.2 the above did not print the access logs (i.e. GET /). I needed to add

logging.getLogger("uvicorn.access").handlers = [intercept_handler]

Hi, Im able to get this working. However default uvicorn logs are not being shown. The logs shows only if its explicitly logged to console.
Am i missing anything here ? thanks.

Hello there! I not recommend to use loguru anymore. If you want use custom formatting and other cool features, see this new example with structlog

@nkhitrov what is the reason of not using loguru?

1. it can not work with libraries that use default logging handlers (sentry-sdk) out the box because loguru write to sdtout directly (without logging)
2. when you have error in formatter function, loguru crashes without any useful info

structlog is more powerful library. you can write your own processors to modify logs and use plugins

@nkhitrov

1. https://docs.sentry.io/platforms/python/integrations/loguru/
2. if that's it, you haven't convinced me)

@nosid91

1. docs.sentry.io/platforms/python/integrations/loguru

Check dates.
Sentry sdk ~6 months ago
My comment ~8 months ago

2. if that's it, you haven't convinced me)

It is your choice. I don't have a goal to convince anyone. I'm just sharing my knowledge and the problems I've discovered.

Great work, thanks for sharing!

It still works, thanks for sharing!