Abstract Base Classes (ABC)

• An Abstract Base Class (ABC) is a class that cannot be instantiated on its own. It is designed to define a common interface (a set of method names and signatures) that subclasses must implement.
• Polymorphism occurs when different subclasses implement these methods in different ways, and code can work with any of the subclasses interchangeably through the abstract base class interface.

• An abstract class is a class that contains only a list of methods and is used to enforce method implementation in the inheriting classes
  
  
• An abstract method is a method that has a declaration but does not have an implementation
  
  
• Import Abstract Base Class

          import ABC

• Import Abstract Base Class
  • The @abstractmethod decorator is used to define an abstract method within an abstract base class (ABC)

 

How to Define an Abstract Base Class

• Python provides the abc module for this.

• ABC is the base class for all abstract classes.
• @abstractmethod is used to mark methods that must be implemented in a subclass.

 

Example: Polymorphism with ABC

Step 1: Define an abstract base class. 

• This defines the interface all shapes must follow.

Step 2: Create concrete subclasses

• Each subclass provides its own implementation of area() and perimeter().

Step 3: Use them polymorphically

• Even though Rectangle and Circle are different classes, the function print_shape_info() works with both — this is polymorphism through ABCs.

 

isinstance() function

The isinstance() function in Python is used to check if an object is an instance of a specified class or if it is an instance of a subclass of that class.

Here's the general syntax:

isinstance(object, classinfo)

• object: The object to be checked
• classinfo: A class or a tuple of classes to be checked against

 

In the above example, car_instance is an instance of both the Car class and its parent class Vehicle, so isinstance() returns True for both checks.

Output:

True True