8. Principles of Defensive Programming

Defensive programming is about anticipating failure. Write code assuming every dependency, input, or file might fail or be malicious.

Example

def read_number(prompt):
    try:
        value = int(input(prompt))
        if value < 0:
            raise ValueError("Number must be positive.")
        return value
    except ValueError as e:
        print("Error:", e)
        return 0  # Safe fallback

✅ Lesson: Handle failures predictably and safely rather than assuming everything will work.