logs with FastAPI and Uvicorn

Hello,

Thanks for FastAPI, easy to use in my Python projects ! However, I have an issue with logs. In my Python project, I use :

app = FastAPI()
uvicorn.run(app, host="0.0.0.0", port=8000)

And when i test my app I get in the console :

INFO: Started server process...
INFO: Waiting for application startup
INFO: Application startup complete.
INFO: Uvicorn running on http://0.0.0.0:8000 (Press ...)
INFO: 127.0.0.1:41668 - "GET /app/?type=env HTTP/1.1" 304 Not Modified
...

This 5 lines are exactly what I expected. Now I want to have access to these logs because I want to re-format them.

So, if i am right, I have a logger managing :

INFO: Started server process...
INFO: Waiting for application startup
INFO: Application startup complete.
INFO: Uvicorn running on http://0.0.0.0:8000 (Press ...)

and a logger managing :

INFO: 127.0.0.1:41668 - "GET /app/?type=env HTTP/1.1" 304 Not Modified

Is it right ?

I have no problem to get access to the first, I can use :

log1 = logging.getLogger("uvicorn.error")

and then change the formatter, but, for the second I was expecting that :

log2 = logging.getLogger("uvicorn.access")

will do the same, but I am unable to change the formatter for the log :

INFO: 127.0.0.1:41668 - "GET /app/?type=env HTTP/1.1" 304 Not Modified

How I can do that in my Python 3.7 script with FastAPI 0.52.0 and Uvicorn 0.11.3 ? Thank you.

[Jackovic]

Doing :

log_config = uvicorn.config.LOGGING_CONFIG
log_config["formatters"]["access"]["fmt"] = "%(asctime)s - %(levelname)s - %(message)s"
log_config["formatters"]["default"]["fmt"] = "%(asctime)s - %(levelname)s - %(message)s"
uvicorn.run(app, log_config=log_config)

is exactly what I was looking for ! Thank you dbanty.

[dbanty]

This is probably a better question for uvicorn, but I’ll take a stab at answering it. Full disclaimer, this is very likely not the “right way” to do this in uvicorn but…

uvicorn.run takes in a log_config keyword arg which lets you configure the loggers. There is a default log config, you could grab that and override what you need to if the case is simple enough.

log_config = uvicorn.config.LOGGING_CONFIG
log_config["formatters"]["access"]["fmt"] = "%(asctime)s - %(levelname)s - %(message)s"
uvicorn.run(app, log_config=log_config)

The problem with just getting the logger and configuring it seems to be that when you call uvicorn.run, uvicorn applies their logger handlers/formatters. If this is after you tried to apply your own handler, yours would get overridden.

You could also try configuring your logging handlers after FastAPI starts up? Might have better luck as uvicorn won’t be overriding at that point.

@app.on_event("startup")
async def startup_event():
    logger = logging.getLogger("uvicorn.access")
    handler = logging.StreamHandler()
    handler.setFormatter(logging.Formatter("%(asctime)s - %(levelname)s - %(message)s"))
    logger.addHandler(handler)

The way I have that adds a new handler, it won’t override the existing internal one. If that’s okay for you it might be a better approach.