yacl

YACL - Yet Another Color Logger

Overview

YACL is a very simple to use color logger for Python intended to be used for stderr logging. It can be set up with a single function call in existing projects and enables colored logging output with reasonable defaults. Colors are disabled automatically if stderr is not connected to a tty (e.g. on file redirection) or if not supported by the connected terminal. Currently, Linux and macOS are supported.

You can use Markdown style formattings to produce bold and italic text. Additionally, text enclosed in double underscores will be displayed underlined. YACL checks the terminal capabilities and automatically disables unsupported formats.

Additionally, YACL can enable a custom global except hook to colorize Python exceptions tracebacks and automatically start PDB in post mortem mode (so you don't need to run your script with python -m pdb explicitly).

Breaking changes

• From version 0.5.x to 0.6:

  • The function setup_colored_exceptions is now always available, regardless if Pygments is installed or not. However, it will raise an ImportError is Pygments cannot be imported.

• From version 0.4.x to 0.5:

  • Color codes are now applied after the logger created the final logging string with all placeholders replaced.

    Example:

    item_count = 3
    logger.info("Found %d items.", item_count)
    

    Before version 0.5, color codes were applied to the string "Found %d items". Now, color codes are added to the final string "Found 3 items". This requires the library user to rework custom keyword_colors dictionaries but is more flexible for applying color rules.

Installation

YACL is available on PyPI for Python 3.9+ and can be installed with pip:

python3 -m pip install yacl

If you use Arch Linux or one of its derivatives, you can also install yacl from the AUR:

yay -S python-yacl

Usage

Simple

Call setup_colored_stderr_logging after the root logger has been set up, for example:

#!/usr/bin/env python3

import logging
from yacl import setup_colored_stderr_logging


def main():
    logging.basicConfig(level=logging.DEBUG)
    setup_colored_stderr_logging()


if __name__ == "__main__":
    main()

Afterwards, get module level loggers and use them without any further configuration:

import logging


logger = logging.getLogger(__name__)


def my_func():
    logger.debug('Failed to open file "abc"')

You will get an output like:

This example only works if you don't attach any output handlers to loggers other than the root logger as recommended in the Python logging documentation:

If you attach a handler to a logger and one or more of its ancestors, it may emit the same record multiple times. In general, you should not need to attach a handler to more than one logger - if you just attach it to the appropriate logger which is highest in the logger hierarchy, then it will see all events logged by all descendant loggers, provided that their propagate setting is left set to True. A common scenario is to attach handlers only to the root logger, and to let propagation take care of the rest.

Customization

You can pass several arguments to the setup_colored_stderr_logging function to customize the logging behavior:

• logger: The logger which will be configured to print colored logging output to stderr. By default, the root logger is used.

• format_string: The format string to use for logging messages. By default the logging format [%(levelname)s] (%(name)s:%(lineno)s:%(funcName)s): %(message)s is used.

  Important: All formats must be passed as string types. For example, in the default format, lineno is given as string ((%lineno)s) and not as number ((%lineno)d).

• remove_other_handlers: Bool flag to remove all other output handlers on the given logger. Is set to true by default to avoid duplicate logging messages.

• attribute_colors: A dictionary which assigns colors to logging attributes (which are used in the logging format string). This dictionary is merged with the internal defaults:

  from yacl import TerminalColorCodes
  
  _attribute_colors = {
      "funcName": TerminalColorCodes.blue,
      "lineno": TerminalColorCodes.yellow,
      "name": TerminalColorCodes.cyan,
  }
  

• keyword_colors: A dictionary which assigns colors to a given regular expressions. This setting can be used to highlight expressions in the logging messages. This dictionary is merged with the internal defaults:

  from yacl import TerminalColorCodes
  
  keyword_colors = {
      r"\bcritical( error)?\b": TerminalColorCodes.red + TerminalColorCodes.blink + TerminalColorCodes.bold,
      r"\bdebug(ged|ging)?\b": TerminalColorCodes.green + TerminalColorCodes.bold,
      r"\berror\b": TerminalColorCodes.red + TerminalColorCodes.bold,
      r"\bfail(ed|ing)?\b": TerminalColorCodes.red + TerminalColorCodes.bold,
      r"\binfo\b": TerminalColorCodes.blue + TerminalColorCodes.bold,
      r"\bwarn(ed|ing)?\b": TerminalColorCodes.yellow + TerminalColorCodes.bold,
      r'"[^"]*"': TerminalColorCodes.yellow,
      r"\*([^*]+)\*": TerminalColorCodes.italics,
      r"\*\*([^*]+)\*\*": TerminalColorCodes.bold,
      r"__([^_]+)__": TerminalColorCodes.underline,
      r"`([^`]+)`": TerminalColorCodes.standout,
  }
  

  Example: Pass a dictionary

  {
      r"'[^']*'": TerminalColorCodes.green + TerminalColorCodes.italics,
  }
  

  to highlight strings in single quotes with green color and italic font (if supported by the Terminal).

• level_colors: A dictionary which assigns colors to logging levels (DEBUG, INFO, ...). This dictionary is merged with the internal defaults:

  from yacl import TerminalColorCodes
  
  level_colors = {
      "DEBUG": TerminalColorCodes.green + TerminalColorCodes.bold,
      "INFO": TerminalColorCodes.blue + TerminalColorCodes.bold,
      "WARNING": TerminalColorCodes.yellow + TerminalColorCodes.bold,
      "ERROR": TerminalColorCodes.red + TerminalColorCodes.bold,
      "CRITICAL": TerminalColorCodes.red + TerminalColorCodes.blink + TerminalColorCodes.bold,
  }
  

Colored Exceptions

If Pygments is installed, YACL can generate colored exception tracebacks. You can force to install Pygments as a YACL dependency with the colored_exceptions extra:

python3 -m pip install 'yacl[colored_exceptions]'

The function setup_colored_exceptions needs to be called once (for example after setup_colored_stderr_logging) to install a custom Python excepthook. It takes an optional bool parameter dark_background which can be set to True to activate brighter colors on dark terminal backgrounds. A full example is:

#!/usr/bin/env python3

import logging
from yacl import setup_colored_exceptions, setup_colored_stderr_logging


def main():
    logging.basicConfig(level=logging.DEBUG)
    setup_colored_stderr_logging()
    setup_colored_exceptions()


if __name__ == "__main__":
    main()

Set the environment variable YACL_ENABLE_COLORED_EXCEPTIONS to 1 to always enable colored exceptions on yacl import. With this activation mode, YACL_DARK_BACKGROUND can be used to control the color scheme.

Note: Starting from Python 3.13, Python has built-in support for colored exception tracebacks. Running setup_colored_exceptions on Python 3.13 or newer has no effect.

PDB post mortem hook

Run setup_pdb_debugging to install a PDB post mortem hook. If your program crashes and is run in a terminal window, you will be dropped into the PDB shell. This allows you to analyze the program state which led to the crash.

Set the environment variable YACL_ENABLE_PDB to 1 to always enable PDB post mortem debugging on yacl import.

Enable colored exceptions and PDB post mortem mode without source code modification

If you would like to use YACL's colored exceptions and / or PDB post mortem debugging without adding it to your project's source code, you can add it to the startup script of your virtual environment. For this, define an enable-yacl function in your shell's startup file (~/.bashrc or ~/.zshrc):

enable-yacl () {
    local site_packages_directory

    if [[ -z "${VIRTUAL_ENV}" ]]; then
        >&2 echo "Please activate a virtual environment first."
        return 1
    fi

    pip install 'yacl[colored_exceptions]' 'git+https://github.com/pdbpp/pdbpp.git' && \
    site_packages_directory="$(python -c 'import site; print(site.getsitepackages()[0])')" && \
    echo 'import yacl' >"${site_packages_directory}/sitecustomize.py"
}

Run enable-yacl to install YACL and pdb++ into the currently activated virtual environment and load yacl on interpreter startup. Now, you can use the environment variables YACL_ENABLE_COLORED_EXCEPTIONS and YACL_ENABLE_PDB (see the explanations in the previous sections) to control the behavior of YACL.

Contributing

Please open an issue on GitHub if you experience bugs or miss features. Please consider to send a pull request if you can spend time on fixing the issue yourself. This project uses pre-commit to ensure code quality and a consistent code style. Run

make git-hooks-install

to install all linters as Git hooks in your local clone of yacl.