🚀 TL;DR

This article explains key software design principles (SOLID + DRY +
KISS) with a real-world Python example.\
You'll also find step-by-step code, a GitHub repo with automation, and a
short guide to present this as a 5-minute video. 🎥

📌 Outline

1. Why software design principles matter 🤔\
2. Key principles (SOLID, DRY, KISS, YAGNI) 📚\
3. Python example: Order Processing System 🐍\
4. Refactoring with design principles applied ✨\
5. GitHub repo structure & CI/CD automation ⚙️

1️⃣ Why software design principles matter 🤔

• 🔧 Maintainability → Easier to update and fix bugs.\
• ♻️ Reusability → Write once, use multiple times.\
• 📈 Scalability → Design that grows with your app.\
• 👩‍💻 Team collaboration → Principles help everyone understand and extend code.

2️⃣ Core Design Principles 📚

• SOLID → Five core OOP principles:
  • S: Single Responsibility\
  • O: Open/Closed\
  • L: Liskov Substitution\
  • I: Interface Segregation\
  • D: Dependency Inversion
• DRY → Don't Repeat Yourself\
• KISS → Keep It Simple, Stupid\
• YAGNI → You Ain't Gonna Need It

3️⃣ Python Example: Order Processing System 🐍

❌ Bad code (violates SRP, DRY):

class Order: def __init__(self, items): self.items = items def calculate_total(self): return sum(item['price'] for item in self.items) def save_to_db(self): print("Saving order to database...") def send_email(self): print("Sending email to customer...") 

👉 Problem: One class is doing everything (violates SRP).

✅ Refactored code with design principles:

class Order: def __init__(self, items): self.items = items def calculate_total(self): return sum(item['price'] for item in self.items) class OrderRepository: def save(self, order: Order): print(f"Saving order with total {order.calculate_total()} to database...") class EmailService: def send_order_confirmation(self, order: Order): print(f"Email sent for order total: {order.calculate_total()}") # Usage items = [{"name": "Pizza", "price": 12}, {"name": "Cola", "price": 3}] order = Order(items) repo = OrderRepository() repo.save(order) email = EmailService() email.send_order_confirmation(order) 

✅ SRP: Each class has a single responsibility.\
✅ DRY: No duplicate calculation logic.\
✅ KISS: Simple methods and classes.\
✅ Extensible: Swap EmailService with SMS later (Open/Closed
Principle).

4️⃣ Repo Structure & Automation ⚙️

software-design-principles/ ├─ order.py ├─ tests/ │ └─ test_order.py ├─ requirements.txt ├─ README.md └─ .github/ └─ workflows/ └─ ci.yml 

requirements.txt

pytest==8.3.3 

ci.yml (GitHub Actions)

name: Python CI on: [push, pull_request] jobs: test: runs-on: ubuntu-latest steps: - uses: actions/checkout@v3 - uses: actions/setup-python@v4 with: python-version: '3.11' - run: pip install -r requirements.txt - run: pytest 

🚀Repository link
🔑Repository to Practice