We Need to Talk About Protocols in Python

Python has matured significantly, and developers need modern tools. The language now offers Protocols as a healthy alternative to Abstract Base Classes (ABC) and inheritance. This feature addresses structural typing through duck typing - the principle that if it walks like a duck and quacks like a duck, then it must be a duck.

The article demonstrates this through a "Home Zoo" example. Traditional Abstract Base Classes require explicit inheritance relationships. When you remove an implemented method from a child class using ABCs, instantiation fails immediately. However, Protocols delay type checking until runtime when methods are actually called.

The key distinction: ABCs use nominal typing (inheritance-based), while Protocols employ structural typing (interface-based). This difference fundamentally changes how coupling works. Classes implementing a Protocol need not inherit from it, reducing dependencies across the codebase.

A significant advantage involves interface segregation. Rather than forcing functions to accept entire objects with many methods, Protocols allow developers to define dedicated interfaces just for specific functions. This aligns with SOLID principles by ensuring code depends only on necessary functionality.

The article acknowledges trade-offs. Protocols sacrifice explicit class hierarchies - documentation becomes less obvious when relationships aren't declared through inheritance. Additionally, when instance creation is paramount, ABCs remain the superior choice since they provide compile-time verification.

The conclusion emphasizes that Protocols excel at instance usage through duck typing, reducing coupling while enabling more flexible, elegant code organization.