Input Validation
Domain: Security
🎯 Motivation
Never trust data from users, files, or network calls. Validating input at the boundary prevents garbage data from causing crashes, security holes, or silent corruption deeper in your code.
📋 Concrete Example
Before processing an age field, check isinstance(age, int) and 0 < age < 150. Reject anything else with a clear error, so invalid values never reach your database or business logic.
🔗 Analogy
A border checkpoint inspects passports before letting travelers in. Without inspection, anyone — including troublemakers — walks straight into the country unchecked.