Your First Decorator — The Basic Pattern

"You've seen what decorators ARE (closures over functions). Now you learn the official Python syntax: @decorator_name. The @ symbol placed above a function definition applies the decorator automatically — it's exactly equivalent to fn = decorator(fn) but cleaner and more readable. Today you build your first real decorators for the budget dashboard: logging, timing, and argument validation. By the end you'll wonder how you ever wrote code without them."