python-colorlog

You can inject colors into your format strings using specific tokens:

Level-based tokens

• log_color: Returns the color associated with the current log record's level.
• <name>_log_color: Returns a secondary color based on the log level (requires secondary_log_colors configuration).

Formatting tokens

• {color}, fg_{color}, bg_{color}: Foreground and background colors.
• bold, bold_{color}, fg_bold_{color}, bg_bold_{color}: Bold/bright colors.
• thin, thin_{color}, fg_thin_{color}: Thin colors (terminal dependent).
• reset: Clears all formatting.

Available color names

• Standard: black, red, green, yellow, blue, purple, cyan, white.
• Bright: light_black, light_red, light_green, light_yellow, light_blue, light_purple, light_cyan, light_white.
• 256-color: Use integers 0-255 (e.g., fg_196, bg_42).

The secondary_log_colors argument allows you to define additional color mappings that can be accessed in the format string using the pattern <name>_log_color. This is useful for highlighting different parts of a log line (like the message) with colors that change based on the log level.

from colorlog import ColoredFormatter

formatter = ColoredFormatter(
	"%(log_color)s%(levelname)-8s%(reset)s %(message_log_color)s%(message)s",
	secondary_log_colors={
		'message': {
			'ERROR': 'red',
			'CRITICAL': 'red'
		}
	}
)

Install the colorlog package from PyPI using pip:

pip install colorlog

To use colorlog, create a colorlog.StreamHandler, set its formatter to colorlog.ColoredFormatter(), and add the handler to your logger.

import colorlog

handler = colorlog.StreamHandler()
handler.setFormatter(colorlog.ColoredFormatter())

logger = colorlog.getLogger('example')
logger.addHandler(handler)

To use colorlog.ColoredFormatter with Python's logging.config.dictConfig, use the () key to specify the class path.

import logging.config

logging.config.dictConfig({
	'formatters': {
		'colored': {
			'()': 'colorlog.ColoredFormatter',
			'format': '%(log_color)s%(levelname)-8s%(reset)s %(blue)s%(message)s'
		}
	}
})

In a .ini configuration file used by fileConfig, define a formatter with class=colorlog.ColoredFormatter.

[formatters]
keys=color

[formatter_color]
class=colorlog.ColoredFormatter
format=%(log_color)s%(levelname)-8s%(reset)s %(bg_blue)s[%(name)s]%(reset)s %(message)s
datefmt=%m-%d %H:%M:%S

Pass a dictionary to log_colors in ColoredFormatter to map log levels to specific colors or color combinations (e.g., red,bg_white).

from colorlog import ColoredFormatter

formatter = ColoredFormatter(
	"%(log_color)s%(levelname)-8s%(reset)s %(blue)s%(message)s",
	log_colors={
		"DEBUG": "cyan",
		"INFO": "green",
		"WARNING": "yellow",
		"ERROR": "red",
		"CRITICAL": "red,bg_white",
	}
)

If you add custom log levels using logging.addLevelName, you can map them to colors in ColoredFormatter by including the level name in the log_colors dictionary.

import logging, colorlog
TRACE = 5
logging.addLevelName(TRACE, 'TRACE')

formatter = colorlog.ColoredFormatter(log_colors={'TRACE': 'yellow'})
handler = logging.StreamHandler()
handler.setFormatter(formatter)

logger = logging.getLogger('example')
logger.addHandler(handler)
logger.setLevel('TRACE')
logger.log(TRACE, 'a message using a custom level')