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I know that default level for root logger is warning (30). If I create a non-root logger and if there is no handler defined on that, then the logger will use the level of the root logger (and handler of the root logger). What is the handler level for the root handler?

#assume no root logger is configured and below code gets the non-root logger for the module logger = logging.getLogger(__name__) #get effective level - this is inherited from the root logger print(logger.getEffectiveLevel()) #set the level for this logger to 10 logger.setLevel(10) #print level which shows 10 print(logger.getEffectiveLevel()) logger.info('this does not get logged') logger.warning('this gets logged')

How can I get info to print?

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  • There are 2 levels: the level of the logger (which you set to 10) and the level of the handler. Idk the default level of the default handler for a new named logger but if it is higher than DEBUG then that explains it. See this question. Commented Oct 21, 2019 at 12:03
  • You haven't registered any handlers. Use logging.basicConfig() to create a default stream handler on the root logger. Commented Oct 21, 2019 at 12:18
  • This article has some more detail in addition to my answer below: realpython.com/python-logging-source-code Commented Oct 21, 2019 at 17:22

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The logger doesn't have any handlers explicitly attached to it by default:

>>> logger.handlers []

However, in the .callHandlers() method, the logging module will actually fall back to a lastResort handler that has a level of WARNING:

_defaultLastResort = _StderrHandler(WARNING) lastResort = _defaultLastResort # .... if (found == 0): if lastResort: if record.levelno >= lastResort.level: lastResort.handle(record)

As indicated in the comments, attaching a handler to logger, either viaa basicConfig() or explicitly through addHandler(), and then setting the level of that handler, will mean the logger doesn't fall back to lastResort.

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Ok so if a handler is attached to a logger (say logger with name as name), then, once the log gets handled by the handler, will it get propagated to the root loggers handler (command line - if no root handler is configured)?
I mean - in presence of handler for a child logger, after the handling log, when the event gets propagated to the root logger, does it fall back to the lastResort handler?
@variable Yes it does fall back to lastResort (and indeed your warning is printed). Keep in mind the lastResort handler has level set to warning so will not print anything below warning, regardless of the level of the logger. This is why your info does not get printed by the lastResort handler. A log record must pass both logger level and handler level. In general, you don't care about the handler level (default is NOTSET which lets everything pass) but in that particular case the handler level is set in the constructor: _StderrHandler(WARNING).
I found this flowchart helpful. In particular, the sub-flowchart on the right describes why your info is not printed: the level of the lastResort handler is higher than info.

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