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Python by Example: Logging

Logging is better than print() for production code—you can control levels, send output to files, and filter by module. The logging module has levels: DEBUG, INFO, WARNING, ERROR, CRITICAL. Set the level to control what appears. Use logging.info(), logging.warning(), etc., instead of print for diagnostic output.

What you'll learn:

  • Configuring with basicConfig()
  • Log levels and when to use each
import logging

# Basic config
logging.basicConfig(level=logging.INFO, format="%(levelname)s: %(message)s")

logging.debug("This won't show (level too low)")
logging.info("Info message")
logging.warning("Warning message")
logging.error("Error message")

Messages at or above the configured level are shown. With level=logging.INFO, DEBUG is hidden. Change to logging.DEBUG to see everything.

To run this program:

$ python source/logging-example.py
INFO: Info message
WARNING: Warning message
ERROR: Error message

Tip: Use DEBUG for development, INFO for normal operation, WARNING for recoverable issues, ERROR for failures.

Try it: Change the level to logging.DEBUG and run again to see the debug message.

Source: logging-example.py

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