Python Design Patterns: When to Use Which Pattern — A Decision Guide

When to Use Which Pattern — A Decision Guide Quick Reference Problem Pattern Category Need exactly one global instance Singleton Creational Create objects without specifying class Factory Creational Complex object construction Builder Creational Incompatible interface Adapter Structural Add behavior without subclassing Decorator Structural Simplify complex subsystem Facade Structural Notify multiple objects of state change Observer Behavioral Swap algorithms at runtime Strategy Behavioral Encapsulate actions with undo support Command Behavioral Pass request through handler chain Chain of Responsibility Behavioral Coordinate async producers & consumers Producer/Consumer Concurrency Protect calls to unreliable services Circuit Breaker Concurrency Decision Flowchart START → Do you need to create objects? │ ├─ YES → Is construction complex (many optional params)? │ ├─ YES → Builder │ └─ NO → Do you need to decouple creation from usage? │ ├─ YES → Factory │ └─ NO → Do you need exactly one i