mplog: Python advanced multiprocessing logging.

example.py

import logging
import multiprocessing
import time

import mplog

FORMAT = '%(asctime)s - %(processName)s - %(levelname)s - %(message)s'
logging.basicConfig(level=logging.DEBUG, format=FORMAT)
existing_logger = logging.getLogger('x')


def subprocess(n):
    existing_logger.info('y')
    logger = logging.getLogger('sub')
    logger.info('Before sleep.')
    time.sleep(0.01)
    logger.info('After sleep.')

    root = logging.getLogger()
    root.debug('Root log message.')


def start_processes(log_queue):
    procs = list()
    for i in xrange(5):
        proc = multiprocessing.Process(target=mplog.logged_call,
                                       args=(log_queue, subprocess, i))
        proc.start()
        procs.append(proc)

    for proc in procs:
        proc.join()


def main():
    existing_logger.info('Before')
    with mplog.open_queue() as log_queue:
        existing_logger.info('In context manager.')
        start_processes(log_queue)
        existing_logger.info('At the end.')

    logging.info('Now really quitting.')


if __name__ == '__main__':
    main()

mplog.py

'''
MIT License

Copyright (c) 2019, Marc Schlaich.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

'''

import contextlib
import multiprocessing
import logging
import threading


def daemon(log_queue):
    while True:
        try:
            record_data = log_queue.get()
            if record_data is None:
                break
            record = logging.makeLogRecord(record_data)

            logger = logging.getLogger(record.name)
            if logger.isEnabledFor(record.levelno):
                logger.handle(record)
        except (KeyboardInterrupt, SystemExit):
            raise
        except EOFError:
            break
        except:
            logging.exception('Error in log handler.')


class MPLogger(logging.Logger):
    log_queue = None

    def isEnabledFor(self, level):
        return True

    def handle(self, record):
        ei = record.exc_info
        if ei:
            # to get traceback text into record.exc_text
            logging._defaultFormatter.format(record)
            record.exc_info = None  # not needed any more
        d = dict(record.__dict__)
        d['msg'] = record.getMessage()
        d['args'] = None
        self.log_queue.put(d)


def logged_call(log_queue, func, *args, **kwargs):
    MPLogger.log_queue = log_queue
    logging.setLoggerClass(MPLogger)
    # monkey patch root logger and already defined loggers
    logging.root.__class__ = MPLogger
    for logger in logging.Logger.manager.loggerDict.values():
        if not isinstance(logger, logging.PlaceHolder):
            logger.__class__ = MPLogger
    func(*args, **kwargs)


@contextlib.contextmanager
def open_queue():
    log_queue = multiprocessing.Queue()
    daemon_thread = threading.Thread(target=daemon, args=(log_queue,))
    daemon_thread.start()
    yield log_queue
    log_queue.put(None)

output.txt

$ python example.py
2013-10-16 09:27:16,526 - MainProcess - INFO - Before
2013-10-16 09:27:16,545 - MainProcess - INFO - In context manager.
2013-10-16 09:27:16,634 - Process-1 - INFO - y
2013-10-16 09:27:16,634 - Process-1 - INFO - Before sleep.
2013-10-16 09:27:16,637 - Process-2 - INFO - y
2013-10-16 09:27:16,638 - Process-2 - INFO - Before sleep.
2013-10-16 09:27:16,644 - Process-1 - INFO - After sleep.
2013-10-16 09:27:16,644 - Process-1 - DEBUG - Root log message.
2013-10-16 09:27:16,645 - Process-3 - INFO - y
2013-10-16 09:27:16,645 - Process-3 - INFO - Before sleep.
2013-10-16 09:27:16,648 - Process-2 - INFO - After sleep.
2013-10-16 09:27:16,648 - Process-2 - DEBUG - Root log message.
2013-10-16 09:27:16,651 - Process-4 - INFO - y
2013-10-16 09:27:16,651 - Process-4 - INFO - Before sleep.
2013-10-16 09:27:16,655 - Process-3 - INFO - After sleep.
2013-10-16 09:27:16,655 - Process-3 - DEBUG - Root log message.
2013-10-16 09:27:16,661 - Process-4 - INFO - After sleep.
2013-10-16 09:27:16,661 - Process-4 - DEBUG - Root log message.
2013-10-16 09:27:16,684 - Process-5 - INFO - y
2013-10-16 09:27:16,684 - Process-5 - INFO - Before sleep.
2013-10-16 09:27:16,694 - Process-5 - INFO - After sleep.
2013-10-16 09:27:16,694 - Process-5 - DEBUG - Root log message.
2013-10-16 09:27:16,697 - MainProcess - INFO - At the end.
2013-10-16 09:27:16,697 - MainProcess - INFO - Now really quitting.

FYI, commenting on a gist won't notify the author (isaacs/github#21)

That said, this is pretty cool - seems to work on Python 3.6 if you change the xrange() call to just range()

Added MIT License

This lends itself nicely to a standalone repository. You should consider that..