python_logging_cheatsheet.py

import logging
import sys

# ----------- Library code ------------------- #
logger = logging.getLogger(__name__)

# think of this as a global restriction
# even if the handlers want access to lower levels, they don't get it
logger.setLevel(logging.INFO)

# Always attach the null handler
logger.addHandler(logging.NullHandler())


# ----------- Application code, setup logger --------------- #

class LevelFilter(logging.Filter):
    def __init__(self, low, high=None):
        if high is None:
            high = low
        self._low = low
        self._high = high
        logging.Filter.__init__(self)

    def filter(self, record):
        if self._low <= record.levelno <= self._high:
            return True
        return False


formatter = logging.Formatter(
    '%(asctime)s - %(name)s - %(levelname)s - %(message)s')

# DEBUG through INFO goes to file
fh = logging.FileHandler('/tmp/debug.log')
fh.setFormatter(formatter)
fh.addFilter(LevelFilter(logging.DEBUG, logging.INFO))
logger.addHandler(fh)

# WARNING or more go to stderr
sh = logging.StreamHandler(sys.stderr)
sh.setLevel(logging.WARN)
sh.setFormatter(formatter)
logger.addHandler(sh)


# ----------- Application code, use the logger --------------- #
logger.debug("This is debug...")
logger.info("This is information.")
logger.warn("This is a warning.")
logger.error("This is Error!")
logger.critical("This is CRITICAL")