The log file will not be created automatically

[blackAzrael]

from loguru import logger
logger.add("log/waf_api.log",  rotation="00:00", encoding="utf-8", enqueue=True, retention="2 months")
import time
if __name__ == "__main__":

    while True:
        logger.debug("11111")
        time.sleep(1)

When I delete my log file manually when the program is running, the log file waf_api.log will not be created. How can I solve this?
😕

[Delgan]

For optimizations reasons, the file is opened once while starting the logger. The logged messages are then written to the file object. If the file has been deleted, then the file object is still valid but will point to nothing. However, the file will not be recreated because it will not been reopened.

You can use a custom sink to open() the file before each write:

def sink(message):
    with open("log/waf_api.log", "a") as file:
        file.write(message)

logger.add(sink)

Unfortunately, that means you won't be able to use custom arguments like rotation and retention, you will need to re-implement it by yourself.

You could also try to force rotation if file does not exist:

def rotation(message, file):
    return not os.path.isfile(file.name)

logger.add("log/waf_api.log", rotation)

However, it generates an error because Loguru does not expect the file to be deleted.

Obviously, the easiest solution is to avoid deleting a file in use if possible. As we can see, this raises some problems.

[blackAzrael]

If the log file is lost in some cases, it will not be able to record the log. Will this problem be solved in the future?

[Delgan]

I don't really plan to integrate it to Loguru. If your file is likely to be deleted, you'll have to create your own handler and use it to re-open the file.

[blackAzrael]

If in a large-scale project, the operator mistakenly deletes some log files, and re-creates the file with the same name. The log cannot be written, which will lose a lot of logs. I think this is a problem.🥺

[Delgan]

Well... I was going to suggest you to use the WatchedFileHandler from standard library or WatchedRotatingFileHandler from third party. Since Loguru supports standard Handler, it should work fine.

However, that made me realize this could easily be integrated to Loguru as a new parameter while adding a file sink.

logger.add("file.log", watch=True)

It shouldn't be too cumbersome, and it is surely useful as demonstrated by your example and by the existence of such handler in the standard library.

I will add it in the next version. Thanks for insisting. 🙂

[Delgan]

The new watch option is implemented on master branch and will be available in next release.

As discussed, if this option is set to True, then Loguru will re-create the file if it detects it has been deleted or modified (if its device or inode changes).