📝 Python Logging – Track Info, Warnings & Errors Efficiently

🧲 Introduction – Why Use Logging in Python?

Debugging with print() is fine—for toy scripts.

But in real-world applications, you need a robust and scalable way to:

• Track what happened (and when)
• Record errors and warnings
• Write logs to files or external systems
• Debug without cluttering production output

That’s where Python’s built-in logging module comes in.

🎯 In this guide, you’ll learn:

• How Python logging works
• Logging levels and use cases
• How to log to a file
• Formatting and configuring logs
• Real-world practices for robust logging

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✅ Getting Started with Python Logging

import logging

logging.basicConfig(level=logging.INFO)
logging.info("This is an info message.")

✅ Output:

INFO:root:This is an info message.

💡 basicConfig() sets up the logging system and configures the default behavior.

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🔢 Logging Levels Explained

Python logging uses levels to classify the importance of events:

Level	Method	Use For
DEBUG	logging.debug()	Detailed information for debugging
INFO	logging.info()	Confirmation that things work as expected
WARNING	logging.warning()	Something unexpected, non-breaking
ERROR	logging.error()	A serious problem, but still running
CRITICAL	logging.critical()	Fatal error, app may crash

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🧪 Example – Logging at Multiple Levels

logging.debug("Debugging message")
logging.info("Info message")
logging.warning("Warning message")
logging.error("Error message")
logging.critical("Critical error")

💡 By default, only WARNING and above are shown unless you set a lower level.

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🗂️ Logging to a File

logging.basicConfig(
    filename="app.log",
    level=logging.DEBUG,
    format="%(asctime)s - %(levelname)s - %(message)s"
)

logging.info("File logging initialized.")

✅ Creates app.log file with:

2025-05-14 21:00:00,123 - INFO - File logging initialized.

💡 Great for persistent error tracking, especially in production.

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🔧 Logging Formatter and Custom Configuration

✅ Format Tokens:

Token	Description
%(asctime)s	Timestamp
%(levelname)s	Log level
%(message)s	Log message
%(name)s	Logger name
%(lineno)d	Line number
%(funcName)s	Function name

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🧱 Advanced Configuration with logging.config

import logging.config

logging.config.dictConfig({
    'version': 1,
    'formatters': {
        'detailed': {
            'format': '%(asctime)s %(name)s [%(levelname)s]: %(message)s'
        }
    },
    'handlers': {
        'file': {
            'class': 'logging.FileHandler',
            'filename': 'advanced.log',
            'formatter': 'detailed'
        }
    },
    'root': {
        'handlers': ['file'],
        'level': 'INFO'
    }
})

logging.info("Configured with dictConfig.")

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🧰 Real-World Use Case – Error Logging in try/except

try:
    x = 1 / 0
except ZeroDivisionError as e:
    logging.error("Exception occurred", exc_info=True)

✅ Output with traceback:

ERROR:root:Exception occurred
Traceback (most recent call last):
  ...
ZeroDivisionError: division by zero

💡 Use exc_info=True to include full stack trace.

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📘 Best Practices for Logging

✅ Do This	❌ Avoid This
Use appropriate levels (info, error)	Logging everything as print()
Use log files for long-term tracking	Overwriting the same log file
Include traceback using exc_info=True	Hiding errors with vague messages
Use RotatingFileHandler for big files	Letting logs grow indefinitely

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📌 Summary – Recap & Next Steps

Python’s logging module provides a powerful, scalable way to track events, debug issues, and keep your programs stable in production.

🔍 Key Takeaways:

• ✅ Use logging.debug(), info(), warning(), error(), and critical() as needed
• ✅ Configure logging with basicConfig() or dictConfig()
• ✅ Use log files and rotation for persistent tracking
• ✅ Always log exceptions using exc_info=True

⚙️ Real-World Relevance:
Used in web apps, data pipelines, automation scripts, and enterprise software to monitor health and troubleshoot effectively.

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❓ FAQ – Python Logging

❓ What’s the default logging level?

✅ WARNING. Only messages of warning, error, and critical are shown by default.

❓ How do I log to both console and file?

✅ Use multiple handlers:

handler1 = logging.StreamHandler()
handler2 = logging.FileHandler("app.log")

Then add both to the logger.

❓ Can I rotate logs automatically?

✅ Yes. Use RotatingFileHandler or TimedRotatingFileHandler from logging.handlers.

❓ Is logging better than print for debugging?

✅ Absolutely. Logging provides levels, formats, file output, and error tracebacks.

❓ Can I suppress logs in production?

✅ Yes. Set a higher logging level like WARNING or ERROR using basicConfig(level=logging.ERROR).

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