background

-There was talk of wanting to separate log files for each log level in Python. ・ In the first place, I used the logging library in a hurry and didn't understand it properly.

Let's solve the problem while moving our hands and organizing.

review

import logging

logging.basicConfig(format='%(asctime)s   %(message)s', datefmt='%m/%d/%Y', filename = './basic.log')
logging.warning('basic.Recorded in log with date.')
logging.basicConfig(filename = './not-appeared.log')
logging.warning('basicConfig only works the first time after booting, so not-appeared.No log is generated.')

root_logger = logging.getLogger('')
root_logger.setLevel(logging.ERROR)
root_logger.error('A root logger has been set up to record ERROR levels and above. basic.It will continue to appear in the log. I haven't specified a handler, so I can't find anything else.')

root_logger.addHandler(logging.StreamHandler())

root_logger.error('This will appear on the console. The format specified in basicConfig is ignored.')
root_logger.warning('Since the log level is low, it does not appear on the console. If ignored, basic.It does not appear in the log.')

critical_handler = logging.FileHandler('./critical.log')
critical_handler.setLevel(logging.CRITICAL)
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
critical_handler.setFormatter(formatter)
root_logger.addHandler(critical_handler)

root_logger.critical('Added a handler that records only CRITICAL. Added date and level name.')
root_logger.error('Although this appears on the console, it is critical because the log level is low.It does not appear in the log.')

second_logger = logging.getLogger('second')
second_logger.setLevel(logging.WARNING)
second_logger.addHandler(logging.StreamHandler())

second_logger.warning('Add a logger and put it on the console. basic.In addition to log, it appears twice on the console with the root logger.')

second_logger.propagate = False

second_logger.warning('If you reject propagate, it will not be transmitted upstream, this is second_Only one logger is available.')

Looking back and examining

-Can be inherited in multiple stages based on the root logger. -Multiple handlers can be set for each. -Log levels can be set for loggers and handlers respectively. -However, since both are lower thresholds, it is not possible to filter only specific logs as required.

solution

If you use a filter, you can filter by calling the log record (instance of the log message) as an argument and returning the boolean value each time you log.

I referred to this Stack Overflow post. As # 1 says, I agree that extracting only a specific level does not make it readable by humans.

python logging specific level only

`log_file_by_level.py`


import logging

class LoggingFilter(object):
    """A filter that leaves only a specific log level"""
    def __init__(self, level):
        self.__level = level

    def filter(self, logRecord):
        #Remove the level setting to handler and here== self.__It should be possible to set it to level.
        return logRecord.levelno <= self.__level

def set_handler(loglevel, filename):
    #Common log format
    log_format = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s', datefmt='%Y-%m-%d %H:%M:%S')
    handler = logging.FileHandler(filename)
    handler.setLevel(loglevel)
    handler.setFormatter(log_format)
    handler.addFilter(LoggingFilter(loglevel))
    logger.addHandler(handler)

logger = logging.getLogger(__name__)
#Specify the minimum level to be recorded in the app.
logger.setLevel(logging.DEBUG)
set_handler(logging.WARN, './warning.log')
set_handler(logging.INFO, './info.log')

`main.py`


from log_file_by_level import logger

logger.warning('I warn you.')
logger.info('Please be informed that this is just a test.')
logger.error('Found error on your smile.')

reference

-Python logging specific level only -Logging HOWTO — Python 3.6.1 documentation

Python logging standard library for file output by log level