使用带有 basicConfig 和 RotatingFileHandler 的日志记录

Question

I'm trying to use logging.basicConfig to log everything and logging.hanlers.RotatingFileHandler to have a maxBytes=1000000 and backupCount=5 . The problem is that when I use RotatingFileHandler it'll log some duplicate outputs as well. I tried removing basicConfig and only using RotatingFileHandler but it didn't log every message I wanted.

example:

logging.basicConfig(format=f, datefmt=date, level=lvl, filename=file_name)
handler = logging.handlers.RotatingFileHandler(file_name, maxBytes=1000000, backupCount=5)
logging.getLogger('').addHandler(handler)

I changed that to remove basicConfig by:

handler = logging.handlers.RotatingFileHandler(file_name, maxBytes=1000000, backupCount=5)
handler.setFormatter(f)
handler.setLevel(lvl)
logging.getLogger('').addHandler(handler)

The above didn't work as RotatingFileHandler didn't log every message that I wanted. Why?

Answer 1

The logger that you get from logging.getLogger('') has its logging level set by default to logging.WARNING . You need to set the desired level on the logger itself as well as on each handler you associate with it to ensure you log the desired messages. Your second code snippet sets the level for the handler but not the logger.

https://docs.python.org/3/library/logging.html#logging.Logger.setLevel

Answer 2

The default level of the root logger is logging.WARNING . This causes messages which are less severe to be ignored (see Logging Levels ). In order for the root logger to delegate all messages, its level needs to be set to logging.NOTSET .

import logging
import logging.handlers

# Change root logger level from WARNING (default) to NOTSET in order for all messages to be delegated.
logging.getLogger('').setLevel(logging.NOTSET)

# Add file rotatin handler, with level DEBUG
rotatingHandler = logging.handlers.RotatingFileHandler(filename='rotating.log', maxBytes=1000, backupCount=5)
rotatingHandler.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
rotatingHandler.setFormatter(formatter)
logging.getLogger('').addHandler(rotatingHandler)

log = logging.getLogger("myApp." + __name__)

log.debug('Hello, debug message.')
log.info('Hello, info message.')
log.warning('Hello, warning message.')
log.error('Hello, error message.')

Answer 3

You can combine the basicConfig and RotatingFileHandler through " logging.Formatter " , the below code snippet shows how to implement that. This will log all the messages and avoid duplicates.

import logging
import logging.handlers

#Set logger with required log level as base 
loggerInstance = logging.getLogger('name_of_logger')
loggerInstance.setLevel(logging.DEBUG)

# Configure the handler with filePath,maxBytes and backupCount
# maxBytes - theMaxSizeOfLogFileInBytes
# backupCount - numberOFBackUpFiles to be created ex: logFile1,logFile2 etc (after log rotation)
handler = logging.handlers.RotatingFileHandler(completeLogFilePathWithFileName,
                                               maxBytes=100000,
                                               backupCount=30)
#Specify the required format                                               
formatter = logging.Formatter('%(asctime)s %(filename)s %(funcName)s %(lineno)d %(levelname)s %(message)s')
#Add formatter to handler
handler.setFormatter(formatter)
#Initialize logger instance with handler
loggerInstance.addHandler(handler)

Use various options in logger to log once the loggerInstance is created.

Ex:

loggerInstance.debug("your debug message") #for debug
loggerInstance.error("your error message") #for error

for detailed documentation follow below link: https://docs.python.org/3/library/logging.handlers.html#rotatingfilehandle