What is an abstract base class?

An abstract base class is a class that cannot be instantiated and is designed to be inherited by other classes. It serves as a blueprint for other classes, providing a common interface, structure, and/or default behavior that can be shared among multiple subclasses.

Abstract base classes have two key features: abstract methods and inheritance. 1. Abstract methods: These are methods that have no implementation in the abstract base class and must be implemented by any subclass that inherits from the abstract base class. They are marked with the keyword 'abstract' to indicate that they don't have a specific implementation in the base class. 2. Inheritance: Subclasses inherit the structure, properties, and default behavior (if any) from the abstract base class, allowing for code reuse and a more organized inheritance hierarchy.

In object-oriented programming (OOP), abstract base classes promote polymorphism, code reuse, and a clear hierarchy by providing a common blueprint for related classes. This helps to reduce code duplication, achieve better separation of concerns, and make the code more maintainable and scalable.

Let's consider a simple example in Python. We have an abstract base class called `Animal` which contains two abstract methods: `sound()` and `habitat()`. ```python from abc import ABC, abstractmethod class Animal(ABC): @abstractmethod def sound(self): pass @abstractmethod def habitat(self): pass class Dog(Animal): def sound(self): return "Woof!" def habitat(self): return "Domesticated" class Fish(Animal): def sound(self): return "Glup-Glup" def habitat(self): return "Aquatic" ``` Here, `Animal` is an abstract base class with two abstract methods, which are later implemented by the `Dog` and `Fish` subclasses. We cannot create an instance of the `Animal` class directly, but we can create instances of the subclasses. This allows us to have a clear hierarchy and share the same interface among different types of animals.