How do I get logger to delete existing log file before writing to it again?

Question

Using the configuration below, my logfile will be called 'test-debug.log' and it will grow infinitely for everytime I run the script. I just want this logfile to contain the log records from the most recent run of the script. The log should be deleted before starting again.

How do I do that?

logger = logging.getLogger('test') #Create a log with the same name as the script that created it
logger.setLevel('DEBUG')


#Create handlers and set their logging level
filehandler_dbg = logging.FileHandler(logger.name + '-debug.log')
filehandler_dbg.setLevel('DEBUG') 


#Create custom formats of the logrecord fit for both the logfile and the console
streamformatter = logging.Formatter(fmt='%(levelname)s:\t%(threadName)s:\t%(funcName)s:\t\t%(message)s', datefmt='%H:%M:%S') #We only want to see certain parts of the message


#Apply formatters to handlers
filehandler_dbg.setFormatter(streamformatter)


#Add handlers to logger
logger.addHandler(filehandler_dbg)

score 68 · Accepted Answer · edited Nov 27 '21 at 12:47

68

Try this:

filehandler_dbg = logging.FileHandler(
   logger.name + '-debug.log', 
   mode='w')

to open the filename in write mode instead of append mode, clobbering logger.name

More information: logging.FileHandler docs, open() and list of modes

edited Nov 27 '21 at 12:47

Ahmad

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answered Feb 06 '14 at 00:46

dmcc

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Thanks, It now works perfectly.. I had actually looked at the documentation for the `filehandler`, but there was no further information about what and why `mode=a` was the default.. Now I think I understand that it comes from `fileIO` syntax or something like that? – Paul H Feb 06 '14 at 01:56
2

Exactly. There's a list of all the modes here: http://docs.python.org/2/library/functions.html#open – dmcc Feb 06 '14 at 02:05
1

its a shame that the docs for logging don't link back to that functions#open page, that would be really useful. – nick fox Feb 16 '18 at 10:30
5

If you're using `logging.basicConfig`, adding `filemode='w'` has the same effect. – Ken Shirriff Jun 05 '20 at 23:30

score 2 · Answer 2 · answered Feb 27 '20 at 06:44

If you are using any external configuration file then pass 'w' for write mode in args of the handler.

[loggers]
keys=root

[logger_root]
level=DEBUG
handlers=file_handler

[handlers]
keys=file_handler

[handler_file_handler]
class=FileHandler
formatter=formatter
args=("../log/test" + time.strftime("%%Y%%m%%d%%H%%M%%S") + '.log', 'w')

[formatters]
keys=formatter

[formatter_formatter]
format=%(asctime)s %(levelname)-5s [%(module)s] %(message)s

How do I get logger to delete existing log file before writing to it again?

2 Answers2