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I have scripts parent.py and child.py (many childs) and I need to have logs for each, so any logging within parent.py should be in parent.log and child.py should be in child.log

I have the below in each script but I get empty logs... why??

#main.py
import child

handler = logging.FileHandler('logs/main.log')
handler.setLevel(logging.DEBUG)
formatter = logging.Formatter("%(asctime)s [%(filename)s:%(lineno)s - % 
(funcName)10s()] %(levelname)s: %(message)s")
handler.setFormatter(formatter)
logger = logging.getLogger(__name__)
logger.addHandler(handler)

child.child_func()
logger.info('testing parent...')


#child.py

handler = logging.FileHandler('logs/child.log')
handler.setLevel(logging.DEBUG)
formatter = logging.Formatter("%(asctime)s [%(filename)s:%(lineno)s - % 
(funcName)10s()] %(levelname)s: %(message)s")
handler.setFormatter(formatter)
logger = logging.getLogger(__name__)
logger.addHandler(handler)

def child_func():
    logger.info('testing child...')

What I need to have is 

#parent.log
{format} testing parent...

#child.log
{format} testing child...
Valeriy
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sql-noob
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2 Answers2

3

The folks above are right about the default level on the loggers. Also, instead of spreading your configuration around everywhere, I find it more manageable to consolidate logging configuration to be early on in the application. See the example below.

Note: I don't expect this to be selected as an answer. I just wanted to point out what I believe is a better way of organizing the code.

main.py

import logging
import child


logger = logging.getLogger(__name__)


def setup_logging():
    main_handler = logging.FileHandler('logs/main.log')
    child_handler = logging.FileHandler('logs/child.log')

    # Note that you can re-use the same formatter for the handlers.
    formatter = logging.Formatter("%(asctime)s [%(filename)s:%(lineno)s - %(funcName)10s()] %(levelname)s: %(message)s")

    main_handler.setFormatter(formatter)
    child_handler.setFormatter(formatter)

    # By default, loggers inherit the level from their parent, so we only need
    # to set the level on the root logger if you want to have only one knob to
    # control the level.
    root_logger = logging.getLogger()
    root_logger.setLevel(logging.DEBUG)

    main_logger = logging.getLogger(__name__)
    child_logger = logging.getLogger('child')
    child_logger.propagate = False

    main_logger.addHandler(main_handler)
    child_logger.addHandler(child_handler)


def main():
    setup_logging()

    child.child_func()
    logger.info('testing parent...')


if __name__ == '__main__':
    main()

child.py

import logging


logger = logging.getLogger(__name__)


def child_func():
    logger.info('testing child...')

Setting up a root logger and a child logger (no main)

Here's an example of setting up the root logger to log to logs/main.log, and the child logger to go to logs/child.log

def setup_logging():
    root_handler = logging.FileHandler('logs/main.log')
    child_handler = logging.FileHandler('logs/child.log')

    # Note that you can re-use the same formatter for the handlers.
    formatter = logging.Formatter("%(asctime)s [%(filename)s:%(lineno)s - %(funcName)10s()] %(levelname)s: %(message)s")

    root_handler.setFormatter(formatter)
    child_handler.setFormatter(formatter)

    # By default, loggers inherit the level from their parent, so we only need
    # to set the level on the root logger if you want to have only one knob to
    # control the level.
    root_logger = logging.getLogger()
    root_logger.setLevel(logging.DEBUG)
    root_logger.addHandler(root_handler)

    child_logger = logging.getLogger('child')
    child_logger.propagate = False
    child_logger.addHandler(child_handler)
John Szakmeister
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  • yes it's working now thank you very much! For some reason though, propagate=False/True does not look to make any difference. I commented that out just to see if child logs will also go to main.log but each script is only logging to its own log... – sql-noob Feb 15 '19 at 15:37
  • Ok it appears I need to chain it correctly if I also want to log to root log https://stackoverflow.com/a/38087696/1890619 – sql-noob Feb 15 '19 at 16:17
  • Yeah, you might actually want to setup the root logger to be your main file (or something like that) if you want everything to go to main.log and just have the child stuff go somewhere else. I updated the answer to include an example of what that would look like. I think it's also worth taking a look at [logging.basicConfig()](https://docs.python.org/2.7/library/logging.html#logging.basicConfig) as an easy way to setup the root logger too (though you'd still need to do some additional steps to get the separate child logger). – John Szakmeister Feb 15 '19 at 20:08
1

You can set severity-level on both handlers and loggers - I believe the logger is set to logging.WARNING by default, so you would only get warning-logs using your code.

You can read more in this thread: What is the point of setLevel in a python logging handler?

import logging
import child

handler = logging.FileHandler('logs/main.log')
formatter = logging.Formatter("%(asctime)s [%(filename)s:%(lineno)s - %(funcName)10s()] %(levelname)s: %(message)s")
handler.setFormatter(formatter)
logger = logging.getLogger(__name__)
logger.addHandler(handler)
logger.setLevel(logging.DEBUG)       # <-- changed 
child.child_func()
logger.info('testing parent...')
logger.warning('testing parent...')
logger.debug('testing parent...')

#child.py
import logging

handler = logging.FileHandler('logs/child.log')
formatter = logging.Formatter("%(asctime)s [%(filename)s:%(lineno)s - %(funcName)10s()] %(levelname)s: %(message)s")
handler.setFormatter(formatter)
logger = logging.getLogger(__name__)
logger.addHandler(handler)
logger.setLevel(logging.DEBUG)      # <-- changed
def child_func():
    logger.info('testing child...')
    logger.warning('testing child...')
    logger.debug('testing child...')
Jeppe
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