Adding custom logging handler to uvicorn.error does not work when running with fastapi run

[BreezeWhite]

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Example Code

import logging
from fastapi import FastAPI


class CustomHandler(logging.StreamHandler):
    def emit(self, record):
        print('No way')


my_handler = CustomHandler()
my_handler.setLevel(logging.ERROR)
uvi_err_logger = logging.getLogger('uvicorn.error')
uvi_err_logger.addHandler(my_handler)

app = FastAPI()

@app.get('/test')
async def test():
    raise ValueError('ohoh')  # This should trigger the error message and print out 'No way' in the terminal

Description

When I am using the custom logging handler, inserting the handler under uvicorn.error, then run the app with fastapi dev, it works fine that prints out "No way" to the terminal. But it fails when running with fastapi run. I looked through the code but cannot find any clue about the why the behaviors are different. This problem is very hard to notice about, and it's been two months later when I finally realized that I've not receiving any error messages from our system...

Operating System

Linux

Operating System Details

This problem happens on every platform.

Python Version

3.11.2

Additional Context

No response

[skaaptjop]

Try removing the existing log handlers before adding your custom one

uvi_err_logger = logging.getLogger("uvicorn.access")
   if uahandlers := uvi_err_logger.handlers:
      uvi_err_logger.removeHandler(uahandlers[0])
uvi_err_logger.addHandler(my_handler)

I do this sort of thing fairly often when I deploy web apps to google cloud in order to reduce the amount of redundant request logging.

[skaaptjop]

Also, look at #15 (reply in thread)
That worked for me although I haven't bothered yet to find out why

[BreezeWhite]

The lifespan approach does work, though pretty weird 😂

[keatonLiu]

The lifespan approach does work, though pretty weird 😂

That's because when you call uvicorn.run(), the logging settings are overwritten if you put the init logic at top of your file.