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)

Solution 1

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

Solution 2

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

Comments

[Paul H]

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?

[dmcc]

Exactly. There's a list of all the modes here: docs.python.org/2/library/functions.html#open

[nick fox]

its a shame that the docs for logging don't link back to that functions#open page, that would be really useful.

[Ken Shirriff]

If you're using logging.basicConfig, adding filemode='w' has the same effect.