Py Design Patterns — Free Python Tutorial

TL;DR: Learn Py Design Patterns in Python with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Py Design Patterns in Python

Design patterns are proven, reusable solutions to commonly recurring software design problems. They are not copy-paste code — they are blueprints you adapt to your context.

Creational patterns control object creation: Singleton (only one instance ever), Factory (create objects without specifying exact class), Builder (construct complex objects step by step).

Structural patterns organize code: Decorator (add behaviour dynamically — Python has native @decorator syntax for this), Adapter (make incompatible interfaces work together), Facade (simple interface over a complex subsystem).

Behavioural patterns define communication: Observer/Event (notify subscribers when state changes), Strategy (swap algorithms at runtime), Command (encapsulate actions as objects for undo/redo queues).

# Singleton
class DB:
    _instance = None
    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance

# Observer
class EventBus:
    def __init__(self): self._subs = {}
    def subscribe(self, event, fn): ...
    def publish(self, event, data): ...

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