What is the point of setLevel in a python logging handler? -

let's have following code:

import logging import logging.handlers  = logging.getlogger('myapp') h = logging.handlers.rotatingfilehandler('foo.log') h.setlevel(logging.debug) a.addhandler(h)  # effective log level still logging.warn print a.geteffectivelevel()  a.debug('foo message') a.warn('warning message') 

i expect setting logging.debug on handler cause debug-level messages written log file. however, prints 30 effective level (equal logging.warning, default), , logs warn message log file, not debug message.

it appears handler's log level being dropped on floor, e.g. it's silently ignored. makes me wonder, why have setlevel on handler @ all?

it allows finer control. default root logger has warning level set, means wont print messages lower level(no matter how handlers' levels set!). but, if set root logger's level debug, indeed message sent log file:

import logging import logging.handlers  = logging.getlogger('myapp') a.setlevel(logging.debug)   # set root's level h = logging.handlers.rotatingfilehandler('foo.log') h.setlevel(logging.debug) a.addhandler(h) print a.geteffectivelevel()  a.debug('foo message') a.warn('warning message') 

now, image want add new handler doesn't record debug information. can setting handler logging level:

import logging import logging.handlers  = logging.getlogger('myapp') a.setlevel(logging.debug)   # set root's level  h = logging.handlers.rotatingfilehandler('foo.log') h.setlevel(logging.debug) a.addhandler(h)  h2 = logging.handlers.rotatingfilehandler('foo2.log') h2.setlevel(logging.warning) a.addhandler(h2)  print a.geteffectivelevel()  a.debug('foo message') a.warn('warning message') 

now, log file foo.log contain both messages, while file foo2.log contain warning message. interested in having log file of error-level messages, add handler , set level logging.error, using same logger.

you may think of logger logging level global restriction on messages "interesting" given logger and handlers. messages considered logger afterwards sent handlers, perform own filtering , logging process.