FastAPI + Uvicorn + loguru configuration

logger.py

"""Classes and functions to customize logs."""

import logging
import sys

from loguru import logger

from app.config import AppSettings  # originaly this is BaseSettings from Pydantic


class InterceptHandler(logging.Handler):
    """Logging handler interceptor from loguru documentation.

    For more info see "https://loguru.readthedocs.io/en/stable/overview.html#entirely-compatible-with-standard-logging"
    """

    def emit(self, record: logging.LogRecord) -> None:
        """Log the specified logging record by loguru logger."""
        try:
            # Get corresponding Loguru level if it exists
            level = logger.level(record.levelname).name
        except ValueError:
            level = str(record.levelno)

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

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


def configure_logger(settings: AppSettings) -> None:
    """Add some loggers to loguru and config logging level."""
    logging.getLogger().handlers = [InterceptHandler()]
    logging.getLogger("uvicorn").setLevel(settings.LOG_LEVEL)
    logging.getLogger("uvicorn.asgi").setLevel(settings.LOG_LEVEL)
    logging.getLogger("uvicorn.error").setLevel(settings.LOG_LEVEL)
    logging.getLogger("uvicorn.access").setLevel(settings.LOG_LEVEL)

    logger.configure(
        handlers=[
            {
                "sink": sys.stdout,
                "level": settings.LOG_LEVEL,
                "enqueue": True,
                "format": (
                    "<green>{time:YYYY-MM-DD HH:mm:ss.SSS}</green> | "
                    "<level>{level: <8}</level> | "
                    "<cyan>{name}</cyan>:<cyan>{function}</cyan>:<cyan>{line}</cyan> - <level>{message}</level> | "
                    "<yellow>{extra}</yellow>"
                ),
            },
        ],
    )

main.py

import uvicorn
from uvicorn.config import LOGGING_CONFIG

...

if __name__ == "__main__":
    # NOTE: "app.logger.InterceptHandler" is the path to your logger's InterceptHandler class
    LOGGING_CONFIG.update(
        {
            "loggers": {
                "handlers": {"default": {"class": "app.logger.InterceptHandler"}}
            }
        }
    )
    uvicorn.run(
        "app.main:app",
        ...
        log_config=LOGGING_CONFIG,
    )

# Log example:
# 2024-03-13 13:13:12.997 | INFO     | uvicorn.main:run:522 - Will watch for changes in these directories: ['/webapp'] | {}
# 2024-03-13 13:13:12.998 | INFO     | uvicorn.main:run:581 - Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit) | {}
# 2024-03-13 13:13:12.998 | INFO     | uvicorn.supervisors.basereload:run:51 - Started reloader process [1] using StatReload | {}
# 2024-03-13 13:13:13.475 | INFO     | asyncio.events:_run:84 - Started server process [9] | {}
# 2024-03-13 13:13:13.475 | INFO     | uvicorn.server:startup:90 - Waiting for application startup. | {}
# 2024-03-13 13:13:13.478 | INFO     | uvicorn.server:startup:90 - Application startup complete. | {}