What are Python abstract base classes used for

Introduction to Abstract Base Classes

Abstract Base Classes (ABCs) in Python, provided by the abc module, allow you to define interfaces that subclasses must implement. They bridge the gap between duck typing and strict interface enforcement.

Defining an ABC

Use ABC as a base class and @abstractmethod to mark required methods:

from abc import ABC, abstractmethod

class Animal(ABC):
    @abstractmethod
    def speak(self):
        pass

class Dog(Animal):
    def speak(self):
        return "Woof!"

Attempting to instantiate Animal directly raises TypeError. This guarantees that every concrete subclass implements the contract. For a deeper dive into object-oriented patterns, check out Python classes and objects.

Practical Use Cases

ABCs are ideal for plugin systems, framework design, and any scenario where you want to document and enforce an expected interface. They also support @abstractproperty and @abstractclassmethod for broader contract definitions.

class DataStore(ABC):
    @abstractmethod
    def connect(self):
        pass

    @abstractmethod
    def fetch(self, query):
        pass

When building robust applications, combining ABCs with proper Python error handling ensures subclasses fail fast and predictably. ABCs promote cleaner architecture and clearer contracts across large codebases.