Python - Abstraction

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Abstraction is one of the important principles of object-oriented programming. It refers to a programming approach by which only the relevant data about an object is exposed, hiding all the other details. This approach helps in reducing the complexity and increasing the efficiency in application development.

There are two types of abstraction. One is data abstraction, wherein the original data entity is hidden via a data structure that can internally work through the hidden data entities. Other type is called process abstraction. It refers to hiding the underlying implementation details of a process.

In object-oriented programming terminology, a class is said to be an abstract class if it cannot be instantiated, that is you can have an object of an abstract class. You can however use it as a base or parent class for constructing other classes.

To form an abstract class in Python, it must inherit ABC class that is defined in the abc module. This module is available in Python's standard library. Moreover, the class must have at least one abstract method. Again, an abstract method is the one which cannot be called, but can be overridden. You need to decorate it with @abstractmethod decorator.

Example

from abc import ABC, abstractmethod
class demo(ABC):
   @abstractmethod
   def method1(self):
      print ("abstract method")
      return
   def method2(self):
      print ("concrete method")

The demo class inherits ABC class. There is a method1() which is an abstract method. Note that the class may have other non-abstract (concrete) methods.

If you try to declare an object of demo class, Python raises TypeError −

   obj = demo()
         ^^^^^^
TypeError: Can't instantiate abstract class demo with abstract method method1

The demo class here may be used as parent for another class. However, the child class must override the abstract method in parent class. If not, Python throws this error −

TypeError: Can't instantiate abstract class concreteclass with abstract method method1

Hence, the child class with the abstract method overridden is given in the following example −

from abc import ABC, abstractmethod
class democlass(ABC):
   @abstractmethod
   def method1(self):
      print ("abstract method")
      return
   def method2(self):
      print ("concrete method")

class concreteclass(democlass):
   def method1(self):
      super().method1()
      return
      
obj = concreteclass()
obj.method1()
obj.method2()

Output

When you execute this code, it will produce the following output −

abstract method
concrete method