Python: File Handler

By using File handler, we can send log messages to a file.

Syntax

logging.FileHandler(filename, mode='a', encoding=None, delay=False)

Argument	Description
filename	Full path of the file
mode	File is opened in this mode. If you don’t specify any mode, file is open in append mode by default.
encoding	Opens file with given encoding.
delay	If delay is true, then file opening is deferred until the first call to emit(). Default value is False.

File handler provides following methods.

Method	Description
close()	Closes the file
emit(record)	Output the record to file

import logging
import sys

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

#Define handler to write to standard output
handler = logging.FileHandler("/Users/harikrishna_gurram/temp.log", encoding="UTF-8")
formatter = logging.Formatter('[%(levelname)s] %(message)s')
handler.setFormatter(formatter)
handler.setLevel(logging.WARN)

#Adding handler to logger
logger.addHandler(handler)

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__"):
    logMessages()
    handler.close()

Run above program, you will get following output in console.

2015-10-23 10:32:33,264 __main__     DEBUG    Debug message
2015-10-23 10:32:33,264 __main__     INFO     Information Message
2015-10-23 10:32:33,264 __main__     WARNING  Warning Message
2015-10-23 10:32:33,264 __main__     ERROR    Error Message
2015-10-23 10:32:33,264 __main__     CRITICAL Critical Message

Following log messages are logged to temp.log.

$ cat temp.log
[WARNING] Warning Message
[ERROR] Error Message
[CRITICAL] Critical Message

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