Bridge Pattern

Overview Software developers often struggle with classes that grow too large and carry too many responsibilities. This tutorial explores how to refactor a messy trading bot into a clean, modular system by using two underrated design patterns: the Template Method and the Bridge Pattern. By the end, you will understand how to standardize a high-level process while allowing specific steps and external dependencies to vary independently. Prerequisites To follow this tutorial, you should have a solid grasp of Python basics, including classes and inheritance. Familiarity with Object-Oriented Programming (OOP) and the concept of Abstract Base Classes is essential, as these serve as the backbone for both design patterns. Key Libraries & Tools * **abc (Abstract Base Classes)**: A built-in Python module used to define blueprints for other classes, ensuring subclasses implement specific methods. * **Trading Bot Example**: A practical context involving cryptocurrency exchanges like Binance and Coinbase to demonstrate real-world decoupling. The Template Method Walkthrough The Template Method defines the skeleton of an algorithm in a base class but lets subclasses override specific steps without changing the overall structure. We start by defining a `TradingBot` that outlines the `check_prices` process. ```python from abc import ABC, abstractmethod class TradingBot(ABC): def check_prices(self, coin): self.exchange.connect() prices = self.exchange.get_market_data(coin) if self.should_buy(prices): print(f"Buying {coin}") if self.should_sell(prices): print(f"Selling {coin}") @abstractmethod def should_buy(self, prices): pass @abstractmethod def should_sell(self, prices): pass ``` By making `should_buy` and `should_sell` abstract, we force specific implementations like an `AverageTrader` or `MinMaxTrader` to define their own logic while keeping the execution flow identical. Bridging Independent Variations While the Template Method handles internal logic steps, the Bridge Pattern decouples an abstraction from its implementation so the two can vary independently. In our bot, the "Exchange" (where data comes from) is a separate concern from the "Trader" (how we decide to trade). ```python class Exchange(ABC): @abstractmethod def connect(self): pass class BinanceExchange(Exchange): def connect(self): print("Connecting to Binance...") ``` We pass an `Exchange` instance into the `TradingBot`. This allows us to swap Binance for Coinbase without touching a single line of our trading strategy logic. Tips & Gotchas Always prioritize cohesion. A class should do one thing well. Avoid the temptation to use these patterns for very simple scripts where a basic function suffices; over-engineering adds unnecessary boilerplate. When debugging, remember that you cannot instantiate abstract classes directly—Python will throw an error if you forget to implement even one abstract method in your subclass.