Design Pattern Application

Purpose

Recognize when to apply established design patterns to create flexible, maintainable, and reusable code structures.

When to Use

• Designing class structures
• Solving recurring design problems
• Refactoring complex code
• Planning extensible architectures

Key Capabilities

1. Pattern Recognition - Identify when patterns apply
2. Pattern Implementation - Correctly implement chosen patterns
3. Trade-off Analysis - Understand pattern costs and benefits

Common Patterns

• Creational: Factory, Builder, Singleton
• Structural: Adapter, Decorator, Facade
• Behavioral: Observer, Strategy, Command

Example - Strategy Pattern

# Problem: Multiple payment methods with different processing logic

class PaymentStrategy:
    def process(self, amount): pass

class CreditCardPayment(PaymentStrategy):
    def process(self, amount):
        # Credit card processing logic
        print(f"Processing ${amount} via credit card")

class PayPalPayment(PaymentStrategy):
    def process(self, amount):
        # PayPal processing logic
        print(f"Processing ${amount} via PayPal")

class Order:
    def __init__(self, payment_strategy: PaymentStrategy):
        self.payment = payment_strategy
    
    def checkout(self, amount):
        self.payment.process(amount)

# Usage
order1 = Order(CreditCardPayment())
order1.checkout(100)

order2 = Order(PayPalPayment())
order2.checkout(50)

Best Practices

• ✅ Use patterns to solve actual problems, not for their own sake
• ✅ Understand the problem before applying a pattern
• ✅ Keep it simple - don't over-engineer
• ❌ Avoid: Using patterns you don't fully understand
• ❌ Avoid: Forcing patterns where they don't fit