Logging & Debugging

Professional applications use logging instead of print statements. Learn to track application behavior and debug effectively.

The logging Module

The logging module is a powerful standard library that tracks events in your software.

Why not just use print?

• Levels: You can categorize messages (Error vs. Info).
• Destinations: Send logs to files, emails, or external services.
• Formatting: Automatically add timestamps and line numbers.

Basic Configuration

import logging

logging.basicConfig(
    level=logging.INFO,
    format='%(asctime)s - %(message)s'
)

Log Levels

Setting the Level

Setting a level ignores all messages below that level.

logger.setLevel(logging.WARNING)
# Now DEBUG and INFO messages are ignored

Logging to File

Logging to File

In production, you want logs saved to a file for later analysis. You use FileHandler for this.

Example

import logging

logging.basicConfig(
    filename='app.log', # Log to this file
    level=logging.INFO
)

logging.info("This is saved to the file")

Application Logger Example

Application Logger Example

When building larger applications, avoid using the root logger (logging.<method>). Instead, create a named logger for each module.

logger = logging.getLogger(__name__)

Quiz

Key Takeaways

✅ Logging is better than print for production code.
✅ Log levels control verbosity (DEBUG to CRITICAL).
✅ Formatters customize log message appearance.
✅ Handlers control where logs go (console, file, etc.).

Keep coding! 🚀