stderr from error and above

Hi,

First of all I would like to congratulate for this awesome library, made my logging experience with Python really simple.

I am not sure if I am using the correct way to setup a logger, what I would like to do is to log to stderr from error level above (error, critical, etc).

My current implementation logs error messages to stdout:

def setup_logger():
    logger.remove()
    logger.add('/tmp/ssh.log', format="{time:YYYY-MM-DD HH:mm:ss} | {level} | {message}", level='DEBUG',
               enqueue=True, retention="14 days")
    logger.add(sys.stdout, colorize=True, format="{time:YYYY-MM-DD HH:mm:ss} | {level} | {message}", level='INFO',
               enqueue=True)

Is there a way do to this?

[Delgan]

Hi @PyAntony.

Defining the level of an handler as the “minimum threshold” for messages to be emitted is a very popular principle among logging libraries. You can look at it this way: by default we don’t want to display debug messages to the user, thus we set the minimal level to “INFO”. However, when something goes wrong, debug messages exist to give more detailed information next to the error messages. If both message are separated in two files, context is lost which makes investigating bugs more challenging. It makes little sense to have the fine grained details without a global view of what is happening.

That’s why in my opinion new arguments like upper_level or levels_allowed should not be added to the add() method. I don’t think this is a good practice when using Loguru.

If you need multiple logs to appear in multiple files (for example), it’s advised to use bind() with a custom filter sink function.

[Delgan]

Indeed. So you want "ERROR" and below to stdout, but "ERROR" and above to stderr?

In this case you may use a function to filter logs emitted to stdout:

logger.add(sys.stdout, filter=lambda record: record["level"].no < 40, level="INFO", ...)