Thursday, October 15

Python logging OnMarkRotatingFileHandler

When there is a need, there is a solution.

As explained in the previous post "The TimedRotatingFileHandler of python logging system", the handler is not doing what I am thinking to do. So I made this new handler OnMarkRotatingFileHandler to fulfill my need. For example, assuming the Interval setting is "Hour":

1, If the program starts at 8:20AM, the TimedRotatingFileHandler will restart a new log file at 9:20AM, but my OnMarkRotatingFileHandler will restart a new log file at 9:00AM.

2, If the previous log file was last modified at 8:58 AM, if you start the program with old handler after 9:58, it will rotate the log; if you start the program before 9:58, say 9:55 the program will just append the log entries into the existing log until 10:55, if your program runs for that long.
With my new handler, now at 9:00AM, when the program starts, the new handler will rotate the log file to generate new log file.


Source code:
#filename: logHandler.py
__author__ = 'ben'

import logging.handlers

class OnMarkRotatingFileHandler(logging.handlers.TimedRotatingFileHandler):

        def __init__(self, filename, when='h', interval=1, backupCount=0, encoding=None, delay=False, utc=False):
            #super().__init__() # in Python 2 use super(D, self).__init__()
            super(OnMarkRotatingFileHandler, self).__init__(filename, when, interval, backupCount, encoding, delay, utc)


        def floor_to(self, num, scale):
            return int(num/scale) * scale


        def computeRollover(self, currentTime):
            temp_result = super(OnMarkRotatingFileHandler, self).computeRollover(currentTime)
            if not self.when.startswith('W'):
                result = self.floor_to(temp_result, self.interval)
            else:
                result = temp_result    # need to find out the first date of time (is it 1970/1/1?), what weekday that is.

            return result


Most methods are inherited from the TimedRotatingFileHandler. The W0/W1.../W6  options are not implemented yet. But you get the ideal.

To use it, place the logHandler.py with your code, then you can either import it and load it as

    import logHandler
    h = logHandler.OnMarkRotatingFileHandler ("filename")
    logger=logging.getLogger('app')
    logger.addHandler(h)


or you can use it in the logging.ini:
    class=logHandler.OnMarkRotatingFileHandler

then load it in logging.config like every other handler does:
    logging.config.fileConfig('logging.ini')


Have fun hacking!


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