Logging: how to set a maximum log level for a handler

Question

With logging library you can log to file. You have to set the file handler log level. Any log with level equal or higher than the specified level will be logged to file.

But what if I want to log errors and exceptions to a file myapp_errors.log, infos to another file myapp_info.log and any other log to another file myapp_debug.log? The only option is to create three loggers?

Answer 1

You can add filters to filehandlers. This way you can redirect specific levels to different files.

import logging

class LevelFilter(logging.Filter):
    def __init__(self, low, high):
        self._low = low
        self._high = high
        logging.Filter.__init__(self)
    def filter(self, record):
        if self._low <= record.levelno <= self._high:
            return True
        return False


logging.basicConfig(level=logging.DEBUG)

log = logging.getLogger('foo')
error_handler = logging.FileHandler('error.log', 'a')
error_handler.addFilter(LevelFilter(40, 40))
warn_handler = logging.FileHandler('warn.log', 'a')
warn_handler.addFilter(LevelFilter(30, 30))
log.addHandler(error_handler)
log.addHandler(warn_handler)

log.debug('debug')
log.info('info')
log.warn('warn')
log.error('error')

Warnings will go to warn.log, errors to error.log. All other levels will not be stored in a file.

Example:

$ python log.py
DEBUG:foo:debug
INFO:foo:info
WARNING:foo:warn
ERROR:foo:error
$ tail -n +1 *.log
==> error.log <==
error

==> warn.log <==
warn

Answer 2

You should take a look at the python documentation. Using multiple logger seems to be the recommended way.