Why is logging behaving this way in python -

so, recently, i've experienced weird behaviour in project, did small test reproduce behaviour. here complete code:

import logging logging import config  config.dictconfig({     'version': 1,     'formatters': {         'fmt_root':    {'format': '[ /        ] - %(levelname)s - %(name)s - %(message)s'},         'fmt_pkg':     {'format': '[ /pkg     ] - %(levelname)s - %(name)s - %(message)s'},         'fmt_pkg_sub': {'format': '[ /pkg/sub ] - %(levelname)s - %(name)s - %(message)s'},     },     'handlers': {         'hnd_root': {             'class': 'logging.streamhandler',             'level': logging.debug,             'stream': 'ext://sys.stdout',             'formatter': 'fmt_root',         },         'hnd_pkg': {             'class': 'logging.streamhandler',             'level': logging.debug,             'stream': 'ext://sys.stdout',             'formatter': 'fmt_pkg',         },         'hnd_pkg_sub': {             'class': 'logging.streamhandler',             'level': logging.debug,             'stream': 'ext://sys.stdout',             'formatter': 'fmt_pkg_sub',         },     },     'root': {         'handlers': ['hnd_root'],         'level': logging.debug,     },     'loggers': {         'pkg': {             'handlers': ['hnd_pkg'],             'level': logging.warning,             'propagate': true,         },         'pkg.sub': {             'handlers': ['hnd_pkg_sub'],             'level': logging.info,             'propagate': true,         },     }, })  logging.getlogger().info('message 1') logging.getlogger('pkg').info('message 2') logging.getlogger('pkg.sub').info('message 3') 

output of small program is:

[ /        ] - info - root - message 1 [ /pkg/sub ] - info - pkg.sub - message 3 [ /pkg     ] - info - pkg.sub - message 3 [ /        ] - info - pkg.sub - message 3 

now, isn't output naturally expect. why "message 2" not logged on root logger (message level info, root accepts debug level) , why "message 3" logged on 'pkg' logger (message level info, pkg accepts warning)?

i did research , found message level checked against logger message posted directly - parent logger levels root not checked, handler levels checked. this seems odd me. there explanation of this? why behave way? use cases this?

ps: behaviour expecting code exact thing if switched handler , logger levels around:

[ /        ] - info - root - message 1 [ /        ] - info - pkg - message 2 [ /pkg/sub ] - info - pkg.sub - message 3 [ /        ] - info - pkg.sub - message 3 

the logger's level used first, go/no go check. because can have multiple handlers logger. example, have filehandler writes disk info , above , smtphandler emails critical.
if passes check log sent loggers handlers, , when propagate set true, it's sent handlers of parent loggers of log called, ignoring level check in loggers.

this way, message 2 not printed @ all, because not pass logger's level check, message 3 print 3 times, because logger set lower level info', , handlers \, pkg , pgk.sub set @ lower level info.

in short, logger level means "should send handlers?" , handler level means "should write disk/console/socket etc.?".

example 1.

logger  | logger level | handler level /       | critical     | debug pkg     | critical     | debug pkg.sub | debug        | debug 

using logging.getlogger('pkg.sub').debug('message 3') print :

[ /pkg/sub ] - debug - pkg.sub - message 3 [ /pkg     ] - debug - pkg.sub - message 3 [ /        ] - debug - pkg.sub - message 3 

example 2.

logger  | logger level | handler level /       | critical     | info pkg     | critical     | debug pkg.sub | debug        | debug 

using logging.getlogger('pkg.sub').debug('message 3') print :

[ /pkg     ] - debug - pkg.sub - message 3 [ /        ] - debug - pkg.sub - message 3 

example 3.

logger  | logger level | handler level /       | critical     | debug pkg     | critical     | info pkg.sub | debug        | debug 

using logging.getlogger('pkg.sub').debug('message 3') print :

[ /pkg/sub ] - debug - pkg.sub - message 3 [ /        ] - debug - pkg.sub - message 3 

in order result want, need setup :

logger  | logger level | handler level /       | debug        | debug pkg     | info         | warning pkg.sub | info         | debug