FastAPI and Loguru

Question

I'm trying to implement a simple use case where I log into the stdout and into a file in a FastApi application. The following code:

def formatter(record):
    print(record)
    # Note this function returns the string to be formatted, not the actual message to be logged
    record["message"] = f"{random.randrange(0, 100)}\n"
    return "{time} | <red>{level}</red> | {extra[trace_id]} | {extra[microservice_name]} | {message}"


fmt = "{time} | <red>{level}</red> | {extra[trace_id]} | {extra[microservice_name]} | {message}"  # Loguru
logger.remove(0)
logger = logger.bind(trace_id=global_vars.trace_id.get(), microservice_name=global_vars.microservice_name.get())
logger.add(f"out-1.log", level="DEBUG", format=formatter, rotation="30 seconds", retention="1 week", colorize=True)
logger.add(sys.stdout, level="DEBUG", format=formatter, colorize=True, diagnose=False)

from fastapi import FastAPI, APIRouter, Depends
from depends import my_depends
from myLogger import logger

app = FastAPI()
router = APIRouter(dependencies=[Depends(my_depends)])


@router.get("/")
def root(name: str):
    logger.info("Got {} as input", name)
    return {"message": name}


app.include_router(router)

import uvicorn
if __name__ == "__main__":
    uvicorn.run("main:app", reload=True)

creates a log file, but after 30 seconds, when it is time to rotate the file and rename the old one with a date in its name, I encounter with PermissionError: [WinError 32] The process cannot access the file because it is being used by another process out-1.log -> out-1.2024-03-14_21-49-52_733426.log

but if I define the file name like this:

logger.add(f"out-{random.randrange(0, 100)}.log", level="DEBUG", format=formatter, rotation="30 seconds", retention="1 week", colorize=True)

the access and rotation works just fine (although it creates 2 files on startup instead of one)

What am I doing wrong?