Refactoring Legacy Code: Lessons Learned

I recently spent a weekend refactoring an old Python script I wrote three years ago. Looking back at your old code is a humbling experience. It works, but it's often ugly.

The Spaghetti Mess

The script was a single 800-line file with global variables everywhere and no functions. It was a nightmare to debug.

The Refactor

1. Modularization: I broke the code into logical functions and moved them into separate files (modules).
2. Type Hinting: I added Python type hints (def process_data(data: list) -> dict:). This caught several subtle bugs where I was passing the wrong data types.
3. Logging: I replaced all print() statements with the logging module. This allows me to toggle debug output without modifying the code.
4. Testing: I wrote basic unit tests using pytest.

The Result

The codebase is now cleaner, easier to read, and robust. It reminded me that "working code" is just the first step. Maintainable code is the real goal. If you have old projects collecting dust, I highly recommend refactoring them. It’s one of the best ways to measure your growth as a developer.