Loguru logger.error writes errors to every log file how to make it write only to error file?

Question

I have recently started using Python Loguru so in order to better understand the library I have created a couple of tests, here's one:

from loguru import logger
import random
loggerEven = logger
loggerEven.add("Even.txt", mode='w', level="INFO")

loggerUneven = logger
loggerUneven.add("UnEven.txt", mode='w', level="ERROR")

x = random.randint(0, 11)
print(x)
if x%2 == 1:
    loggerUneven.error("Uneven")
else:
    loggerEven.info("Even")

So, if the number is even - all is well. However, when I get an uneven number, the log is written both to Even.txt and UnEven.txt files. I tried changing loggerUneven.error to loggerUneven.info and to loggerUneven.success, though in the latter cases the logs are written to Even.txt, is there any way to make files Uneven/error files to be written only to the corresponding file not to every log files?

I have recently started using Python Loguru so in order to better understand the library I have created a couple of tests, here's one:

from loguru import logger
import random
loggerEven = logger
loggerEven.add("Even.txt", mode='w', level="INFO")

loggerUneven = logger
loggerUneven.add("UnEven.txt", mode='w', level="ERROR")

x = random.randint(0, 11)
print(x)
if x%2 == 1:
    loggerUneven.error("Uneven")
else:
    loggerEven.info("Even")

So, if the number is even - all is well. However, when I get an uneven number, the log is written both to Even.txt and UnEven.txt files. I tried changing loggerUneven.error to loggerUneven.info and to loggerUneven.success, though in the latter cases the logs are written to Even.txt, is there any way to make files Uneven/error files to be written only to the corresponding file not to every log files?

Answer 1

loguru loggers don't work quite how you think. Your loggerEven and loggerUneven are both actually the same logger object. So you've added two file sinks to the same logger! This is why you're seeing duplicates.

You can verify this with:

print(loggerEven is loggerUneven)

This will print True, demonstrating that they are both the same logger.

However, although you've added two sinks to the same logger, you've added them with different level arguments. This is why your .error(..) call goes to both files, but your .info(..) call goes to both.

You should look at the filter argument to .add(..).

The loguru docs are excellent and have an example of exactly what you're trying to achieve:

https://loguru.readthedocs.io/en/stable/resources/recipes.html#creating-independent-loggers-with-separate-set-of-handlers