Design Patterns You Should Know

Design patterns are reusable solutions to common problems in software design. They provide a shared vocabulary for developers and help avoid reinventing the wheel. Here are five essential patterns every developer should understand.

Singleton

The Singleton pattern ensures a class has only one instance and provides a global point of access to it.

class DatabaseConnection:
    _instance = None

    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
            cls._instance._connected = False
        return cls._instance

    def connect(self):
        if not self._connected:
            print("Connecting to database...")
            self._connected = True

Observer

The Observer pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified.

class EventEmitter {
    constructor() {
        this.listeners = {};
    }

    subscribe(event, callback) {
        if (!this.listeners[event]) {
            this.listeners[event] = [];
        }
        this.listeners[event].push(callback);
    }

    emit(event, data) {
        (this.listeners[event] || []).forEach(cb => cb(data));
    }
}

Factory Method

The Factory Method pattern delegates the responsibility of object creation to subclasses, keeping your code decoupled.

class Button:
    def render(self):
        pass

class WindowsButton(Button):
    def render(self):
        return "Rendering Windows button"

class MacButton(Button):
    def render(self):
        return "Rendering Mac button"

def create_button(os_type):
    if os_type == "windows":
        return WindowsButton()
    return MacButton()

Strategy

The Strategy pattern lets you define a family of algorithms and make them interchangeable at runtime.

class DiscountStrategy:
    def calculate_discount(self, price):
        pass

class SummerDiscount(DiscountStrategy):
    def calculate_discount(self, price):
        return price * 0.85

class HolidayDiscount(DiscountStrategy):
    def calculate_discount(self, price):
        return price * 0.70

Conclusion

Design patterns aren't rules — they're guidelines born from collective experience. Use them when they fit your problem, but don't force them into places where they don't belong. The best developers know both when to apply patterns and when to simplify.

Design Patterns You Should Know