Design Patterns sind bewährte Lösungen für wiederkehrende Probleme. Sie brauchen nicht alle, aber Sie sollten sie kennen.

Creational¶

Factory Pattern¶

class NotificationFactory: @staticmethod def create(type: str) -> Notification: match type: case ‘email’: return EmailNotification() case ‘sms’: return SMSNotification() case ‘push’: return PushNotification() case _: raise ValueError(f”Unknown type: {type}”)

Behavioral¶

Strategy Pattern¶

from typing import Protocol class SortStrategy(Protocol): def sort(self, data: list) -> list: … class QuickSort: def sort(self, data: list) -> list: return sorted(data) # Simplified class Sorter: def __init__(self, strategy: SortStrategy): self.strategy = strategy def sort(self, data: list) -> list: return self.strategy.sort(data)

Observer Pattern¶

class EventEmitter: def __init__(self): self._listeners = {} def on(self, event, callback): self._listeners.setdefault(event, []).append(callback) def emit(self, event, *args): for cb in self._listeners.get(event, []): cb(*args)

Structural¶

Decorator Pattern (Python native)¶

import functools def retry(max_attempts=3): def decorator(func): @functools.wraps(func) def wrapper(*args, **kwargs): for attempt in range(max_attempts): try: return func(*args, **kwargs) except Exception as e: if attempt == max_attempts - 1: raise return wrapper return decorator @retry(max_attempts=3) def fetch_data(url): return requests.get(url).json()

Wichtigste Erkenntnis¶

Factory zur Erzeugung, Strategy für austauschbare Algorithmen, Observer für Events, Decorator zur Erweiterung. Nicht überentwickeln.