Making Python loggers output all messages to stdout in addition to log file

in stackoverflow ∙ 3 mins read ∙ Tags: Python, Logging, Error-logging Last modified at: Updated:

Making Python loggers output all messages to stdout in addition to log file

  1. Question by Ben
  2. Answer by Milovan Tomašević
    1. UPDATE: color terminal
    2. Recommendation:

Question by Ben

Is there a way to make Python logging using the logging module automatically output things to stdout in addition to the log file where they are supposed to go? For example, I’d like all calls to logger.warning, logger.critical, logger.error to go to their intended places but in addition always be copied to stdout. This is to avoid duplicating messages like:

# file: 'question.py'
mylogger.critical("something failed")
print "something failed"

Answer by Milovan Tomašević

For more detailed explanations - great documentation at that link. For example: It’s easy, you only need to set up two loggers.

# file: 'answer.py'
import sys
import logging

logger = logging.getLogger('')
logger.setLevel(logging.DEBUG)
fh = logging.FileHandler('my_log_info.log')
sh = logging.StreamHandler(sys.stdout)
formatter = logging.Formatter('[%(asctime)s] %(levelname)s [%(filename)s.%(funcName)s:%(lineno)d] %(message)s', datefmt='%a, %d %b %Y %H:%M:%S')
fh.setFormatter(formatter)
sh.setFormatter(formatter)
logger.addHandler(fh)
logger.addHandler(sh)

def hello_logger():
    logger.info("Hello info")
    logger.critical("Hello critical")
    logger.warning("Hello warning")
    logger.debug("Hello debug")

if __name__ == "__main__":
    hello_logger()

Output - terminal:

# file: 'terminal'
[Mon, 10 Aug 2020 12:44:25] INFO [TestLoger.py.hello_logger:15] Hello info
[Mon, 10 Aug 2020 12:44:25] CRITICAL [TestLoger.py.hello_logger:16] Hello critical
[Mon, 10 Aug 2020 12:44:25] WARNING [TestLoger.py.hello_logger:17] Hello warning
[Mon, 10 Aug 2020 12:44:25] DEBUG [TestLoger.py.hello_logger:18] Hello debug

Output - in file:

log in file

Output

UPDATE: color terminal

Package:

# file: 'terminal'
pip install colorlog

Code:

# file: 'answer.py'
import sys
import logging
import colorlog

logger = logging.getLogger('')
logger.setLevel(logging.DEBUG)
fh = logging.FileHandler('my_log_info.log')
sh = logging.StreamHandler(sys.stdout)
formatter = logging.Formatter('[%(asctime)s] %(levelname)s [%(filename)s.%(funcName)s:%(lineno)d] %(message)s', datefmt='%a, %d %b %Y %H:%M:%S')
fh.setFormatter(formatter)
sh.setFormatter(colorlog.ColoredFormatter('%(log_color)s [%(asctime)s] %(levelname)s [%(filename)s.%(funcName)s:%(lineno)d] %(message)s', datefmt='%a, %d %b %Y %H:%M:%S'))
logger.addHandler(fh)
logger.addHandler(sh)

def hello_logger():
    logger.info("Hello info")
    logger.critical("Hello critical")
    logger.warning("Hello warning")
    logger.debug("Hello debug")
    logger.error("Error message")

if __name__ == "__main__":
    hello_logger()

output: enter image description here

Output

Recommendation:

Complete logger configuration from INI file, which also includes setup for stdout and debug.log:

  • handler_file
    • level=WARNING
  • handler_screen
    • level=DEBUG

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