Quick MCQ — Which SOLID principle says “open for extension, closed for modification”?¶

• A) Single Responsibility Principle

• B) Open/Closed Principle

• C) Interface Segregation Principle

Correct: B — Open/Closed Principle.

Exercises (Pyodide-ready)¶

1. Add a LoyaltyDiscount class that gives 5% off and test replacing NoDiscount with it.

2. Implement Logger to collect logs into a list (instead of printing) and return them for assertion.

3. Sketch (as a markdown cell) how you would split Order responsibilities further to follow SRP more strictly.

SOLID Principles¶