Logging and inheritance of loggers' configurations in Python

Question

I come from SLF4J and Log4J, so that might be the reason why I don't get how logging works in Python.

I have the following

---- logging.yaml

version: 1

handlers:

  console:
    class: logging.StreamHandler
    level: DEBUG
    stream: ext://sys.stderr
    formatter: simpleFormatter

  file:
    class: logging.FileHandler
    filename: app.log
    mode: w
    level: DEBUG
    formatter: simpleFormatter

formatters:
  simpleFormatter:
    #class: !!python/name:logging.Formatter
    #class: logging.Formatter
    format: '%(name)s %(asctime)s %(levelname)s %(message)s'
    datefmt: '%d/%m/%Y %H:%M:%S'


root:
  level: INFO
  handlers: [console, file]

mod:
  level: DEBUG

----- mod.py

import logging

def foo ():
    log = logging.getLogger ( __name__ )
    log.debug ( 'Hello from the module' )

---- main.py

from logging.config import dictConfig
import yaml
with open ( 'logging.yaml' ) as flog:
    dictConfig ( yaml.load ( flog ) )

import logging

from mod import foo

if __name__ == '__main__':

    log = logging.getLogger ( __name__ )
    log.debug ( 'Hello from main' )

    foo ()

With the config above, I would expect to see only the message 'Hello from the module' . Instead, nothing is printed. When I set DEBUG for the root logger, both messages are printed.

So, aren't the messages forwarded to the upper loggers? Isn't the mod logger a child of root ? Doesn't the mod logger inherit the handlers configuration? (I've tried to repeat handlers in mod , but nothing changes).

How can I achieve a configuration saying: default level is INFO , the level for this module and sub-modules is DEBUG , everything goes to the handlers defined for root ?

Answer 1

You have a fairly simple error: note that, per the docs , configuration for loggers other than root should be under the loggers key as:

a dict in which each key is a logger name and each value is a dict describing how to configure the corresponding Logger instance

Adding this key and indenting the appropriate lines, to give:

loggers:
  mod:
    level: DEBUG

works as expected:

$ python main.py
mod 20/07/2016 14:35:32 DEBUG Hello from the module

$ cat app.log
mod 20/07/2016 14:35:32 DEBUG Hello from the module