Python Logging and Tracing Cheat Sheet

import logging
logger = logging.getLogger(__name__)

# Use a named logger per module.

import logging

logging.basicConfig(filename='app.log', level=logging.DEBUG)

# Persist logs to disk for debugging after process exit.

logger.warning("Unexpected state", stack_info=True)

# Attach the current stack to a log message.

try:
    risky_call()
except Exception:
    logger.error("Failure", exc_info=True)

# Log a message with traceback details.

import warnings
warnings.simplefilter('default')

# Promote useful warnings during development.

python -W error app.py

# Catch deprecated or risky behavior early.

python -m trace --trace app.py

# Run a script and print executed lines.

python -m trace --count app.py

# Collect line execution counts for scripts.

import faulthandler
import sys

faulthandler.dump_traceback_later(30, repeat=True, file=sys.stderr)

# Emit stack traces after a timeout to catch hangs.

faulthandler.cancel_dump_traceback_later()

# Stop the scheduled faulthandler timeout.