Python: RotatingFileHandler: Rotate log files

RotatingFileHandler is used to rotate log files.

Syntax

logging.handlers.RotatingFileHandler(filename, mode='a', maxBytes=0, backupCount=0, encoding=None, delay=0)

Argument	Description
filename	Full path of the file name.
mode	By default file open in append mode. You can specify the mode.
maxBytes	When the file size about to reach maxBytes, the file is closed and a new file is silently opened for output.
backupCount	If backupCount is non-zero, the system will save old log files by appending the extensions ‘.1’, ‘.2’ etc., If backupCount is 3 and file name is temp.log, then, when this file is filled, it is closed and renamed to temp.log.1, temp.log.2, temp.log.3.
encoding	File opened with given encoding
delay	If delay is true, then file opening is deferred until the first call to emit().

Following are the methods provided by RotatingFileHandler class.

Method	Description
doRollover()¶	Does rollover.
emit(record)	Write record to a file.

Note:

If either of maxBytes or backupCount is zero, rollover never occurs.

import logging
import glob
import logging.handlers

#Define logger
logger = logging.getLogger(__name__)
logging.basicConfig(level=logging.DEBUG, format='%(asctime)s %(name)-12s %(levelname)-8s %(message)s')

LOG_FILENAME="/Users/harikrishna_gurram/temp.log"
#Define handler to write to standard output
handler = logging.handlers.RotatingFileHandler(LOG_FILENAME, maxBytes=1000, backupCount=10)

formatter = logging.Formatter('[%(levelname)s] %(message)s')
handler.setFormatter(formatter)
handler.setLevel(logging.DEBUG)

#Adding handler to logger
logger.addHandler(handler)
logger.propagate = False

def logMessages():
    logger.debug("Debug message")
    logger.info("Information Message")
    logger.warn("Warning Message")
    logger.error("Error Message")
    logger.critical("Critical Message")

if(__name__=="__main__"):
    for i in range(1000):
        logMessages()

    # See what files are created
    logfiles = glob.glob('%s*' % LOG_FILENAME)

    for filename in logfiles:
        print(filename)

Run above program, you will get following output.

/Users/harikrishna_gurram/temp.log
/Users/harikrishna_gurram/temp.log.1
/Users/harikrishna_gurram/temp.log.10
/Users/harikrishna_gurram/temp.log.2
/Users/harikrishna_gurram/temp.log.3
/Users/harikrishna_gurram/temp.log.4
/Users/harikrishna_gurram/temp.log.5
/Users/harikrishna_gurram/temp.log.6
/Users/harikrishna_gurram/temp.log.7
/Users/harikrishna_gurram/temp.log.8
/Users/harikrishna_gurram/temp.log.9

Above program creates 10 log files using rotation.

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