Logging in Python

Table of contents

Basic example
Colorful example

Basic example

In the following example, we specify two handlers. So the messages will output to stdout and to the log_file at the same time.

python

import logging
logger = logging.getLogger()
logger.setLevel(logging.INFO)
formatter = logging.Formatter(
    "%(levelname).1s%(asctime)s [%(module)s:%(lineno)d] %(message)s",
    datefmt="%m%d %H%M%S",
)
stream_handler = logging.StreamHandler(sys.stdout)
stream_handler.setFormatter(formatter)
file_handler = logging.FileHandler(log_file, mode="a")
file_handler.setFormatter(formatter)
logger.handlers = [stream_handler, file_handler]
logging.debug("this is debug")
logging.info("this is info")
logging.warning("this is warning")
logging.error("this is error")
logging.critical("this is critical")

Example output:

I0306 205253 [<ipython-input-4-3747c4192e4e>:17] this is info
W0306 205253 [<ipython-input-4-3747c4192e4e>:18] this is warning
E0306 205253 [<ipython-input-4-3747c4192e4e>:19] this is error
C0306 205253 [<ipython-input-4-3747c4192e4e>:20] this is critical

Colorful example

It has dependency on a non-builtin package, colorma. Also it will be more difficult to tweak the settings. However, colorful messages could be useful in Jupyter.

python

import logging
from colorama import Fore, Back, Style
class ColoredFormatter(logging.Formatter):
    """Colored log formatter."""
    def __init__(
        self, *args, colors: Optional[Dict[str, str]] = None, **kwargs
    ) -> None:
        """Initialize the formatter with specified format strings."""
        super().__init__(*args, **kwargs)
        self.colors = colors if colors else {}
    def format(self, record) -> str:
        """Format the specified record as text."""
        record.color = self.colors.get(record.levelname, "")
        record.reset = Style.RESET_ALL
        return super().format(record)
formatter = ColoredFormatter(
    "[{asctime} {name}] {color}{message}{reset}",
    style="{",
    datefmt="%m%d %H:%M:%S",
    colors={
        "DEBUG": Fore.LIGHTBLACK_EX,
        "INFO": Fore.GREEN + Style.BRIGHT,
        "WARNING": Fore.BLACK + Back.YELLOW + Style.BRIGHT,
        "ERROR": Fore.WHITE + Back.LIGHTRED_EX,
        "CRITICAL": Fore.WHITE + Back.LIGHTMAGENTA_EX,
    },
)
handler = logging.StreamHandler(sys.stdout)
handler.setFormatter(formatter)