Python logging with rich - writing to stderr - plain output when writing to file

Rich is a Python library for writing rich text (with color and style) to the terminal, and for displaying advanced content such as tables, markdown, and syntax highlighted code.

Rich provides RichHandler, a logging handler for python's logging module which will format and colorize text written by the module.

However, RichHandler writes to stdout by default. More specifically, it writes to a rich Console object which, by default, writes to stdout.

To make RichHandler write to stderr by default, you must pass in a Console object which has been configured to write to stderr:

import logging

from rich.console import Console
from rich.logging import RichHandler

DATEFMT = "%Y-%m-%dT%H:%M:%SZ"
FORMAT = "%(message)s"

logging.basicConfig(
    level="NOTSET",
    format=FORMAT,
    datefmt=DATEFMT,
    handlers=[RichHandler(console=Console(stderr=True))],
)

logger = logging.getLogger(__name__)
logger.info("Hello, World!")

This works fine for log output written to a tty, but if you redirect log output to a file you would typically not want to use the same format, eg. not break lines at the width of the screen, etc. One way to achieve this is to only use RichHandler if stderr is connected to a tty.

import logging
import sys

from rich.console import Console
from rich.logging import RichHandler

DATEFMT = "%Y-%m-%dT%H:%M:%SZ"

if sys.stderr.isatty():
    handler = RichHandler(console=Console(stderr=True))
    FORMAT = "%(message)s"
else:
    FORMAT = "%(asctime)s\t%(levelname)s\t%(message)s"
    handler = logging.StreamHandler()

logging.basicConfig(
    level="NOTSET", format=FORMAT, datefmt=DATEFMT, handlers=[handler]
)

logger = logging.getLogger(__name__)
logger.info("Hello, World!")