How to Create an Abstract Class in Python

1. Python 3.4+ - Create an Abstract Class in Python by Inheriting From the ABC Module
2. Python 3.0+ - Create an Abstract Class in Python by Inheriting From the ABCMeta Module
3. Method to Verify if a Class Is Abstract or Not in Python

An abstract class is a restricted class because it cannot be instantiated - you cannot use it to create objects. It can only be inherited from another class.

An abstract class aims to define a common function/behaviour that multiple sub-classes can inherit without having to implement the entire abstract class.

In Python, we can create an abstract class-based in different ways based on the Python version.

Python 3.4+ - Create an Abstract Class in Python by Inheriting From the ABC Module

In Python 3.4, to create an abstract class.

1. Import the ABC (abstract base classes) module.

from abc import ABC, abstractmethod

2. Declare the abstract method using the @abstractmethod decorator.

from abc import ABC, abstractmethod


class ExampleAbstractClass(ABC):
    @abstractmethod
    def abstractmethod(self):
        pass

Below is an example where the Vehicle abstract class has two subclasses, namely, Car and Bike. The classes Car and Bike have their unique implementation.

from abc import ABC, abstractmethod


class Vehicle(ABC):
    @abstractmethod
    def numberofwheels(self):
        pass


class Car(Vehicle):
    def numberofwheels(self):
        print("A Car has 4 wheels")


class Bike(Vehicle):
    def numberofwheels(self):
        print("A Bike has 2 wheels")


C = Car()
C.numberofwheels()

B = Bike()
B.numberofwheels()

Output:

A Car has 4 wheels
A Bike has 2 wheels

Python 3.0+ - Create an Abstract Class in Python by Inheriting From the ABCMeta Module

In Python 3.0+, to create an abstract class.

1. Import the ABCMeta(abstract base classes) module.

from abc import ABCMeta, abstractmethod

2. Declare the abstract method using the @abstractmethod decorator and mention metaclass=ABCMeta.

from abc import ABCMeta, abstractmethod


class Example2AbstractClass(metaclass=ABCMeta):
    @abstractmethod
    def abstractmethod2(self):
        pass

Below is an example.

from abc import ABCMeta, abstractmethod


class Vehicle(metaclass=ABCMeta):
    @abstractmethod
    def numberofwheels(self):
        pass


class Car(Vehicle):
    def numberofwheels(self):
        print("A Car has 4 wheels")


class Bike(Vehicle):
    def numberofwheels(self):
        print("A Bike has 2 wheels")


C = Car()
C.numberofwheels()

B = Bike()
B.numberofwheels()

Output:

A Car has 4 wheels
A Bike has 2 wheels

Method to Verify if a Class Is Abstract or Not in Python

To verify if the class created is indeed an abstract class or not, we should instantiate the class. An abstract class will not allow instantiation and throw an error.

For example, if we instantiate an abstract as below.

x = ExampleAbstractClass()

Then, an error is displayed.

Can't instantiate abstract class ExampleAbstractClass with abstract methods abstractmethod