Logging in Python

From https://realpython.com/python-logging/

Logging to a File

save your logs in an app.log file

import logging
logging.basicConfig(
    filename="app.log",
    encoding="utf-8",
    filemode="a",
    format="{asctime} - {levelname} - {message}",
    style="{",
    datefmt="%Y-%m-%d %H:%M",
)
logging.warning("Save me!")

Displaying Variable Data

use self-documenting expressions:

name = "Samara"
logging.debug(f"{name=}")

To avoid extra evaluation, use the modulo operator (%) for interpolation instead of f-strings”

name = "Samara"
logging.debug("name=%s", name)

Capturing Stack Traces

donuts = 5
guests = 0
try:
    donuts_per_guest = donuts / guests
except ZeroDivisionError:
    logging.error("DonutCalculationError", exc_info=True)

better yet:

try:
    donuts_per_guest = donuts / guests
except ZeroDivisionError:
    logging.exception("DonutCalculationError")

Creating a Custom Logger

Recommended.

Instantiate:

import logging
logger = logging.getLogger(__name__)

Use multiple handlers (with custom levels) to send log to console AND file:

import logging
logger = logging.getLogger(__name__)
logger.setLevel("DEBUG")
console_handler = logging.StreamHandler()
console_handler.setLevel("DEBUG")
logger.addHandler(console_handler)
file_handler = logging.FileHandler("app.log", mode="a", encoding="utf-8")
file_handler.setLevel("WARNING")
logger.addHandler(file_handler)
# show all the logger handlers:
logger.handlers