Abstract in Python

Python Abstract

Understanding Abstract Classes

An abstract class is like a blueprint or concept. It defines what should exist in a class (methods or properties) but does not provide complete implementation. You cannot create objects directly from an abstract class. The purpose is to enforce rules for subclasses, ensuring they implement essential methods.

Analogy: Imagine designing vehicles like Car, Boat, and Plane. You know all vehicles can move(), but each moves differently. You create a blueprint called Vehicle with an abstract move() method. Every subclass must implement it, ensuring consistency while allowing flexibility.

Python Example

from abc import ABC, abstractmethod

# Abstract class (blueprint)
class Person(ABC):
    def __init__(self, first_name, last_name):
        self.first_name = first_name
        self.last_name = last_name

    @abstractmethod
    def display_name(self):
        pass

# Subclass that implements the abstract method
class Student(Person):
    def display_name(self):
        print(f"Student: {self.first_name} {self.last_name}")

# Using the subclass
s = Student("Alice", "Smith")
s.display_name()  # Output: Student: Alice Smith

Step-by-Step Explanation

• Abstract Class (Person): Inherits from ABC and contains an abstract method display_name(). Cannot create objects directly.
• Concrete Subclass (Student): Inherits from Person and implements display_name(). Now objects can be created and used.
• Why useful: Forces all subclasses to implement essential methods, provides a template, ensures consistency across subclasses.

Concrete Class vs Abstract Class

Feature	Abstract Class	Concrete Class
Can you create an object?	No	Yes
Can it have abstract methods?	Yes	No
Purpose	Provide blueprint / enforce rules	Full implementation / ready to use
Example	Person with abstract display_name()	Student with implemented display_name()

Analogy for Beginners

• Abstract class: Blueprint of a house. Cannot live in it, shows what rooms must exist.
• Concrete class: Actual house built from blueprint. Fully usable.

Summary

• Abstract classes define what should be done, not how.
• Subclasses must implement all abstract methods.
• Concrete classes can be instantiated and used.
• Abstract classes help enforce consistency and design rules in large programs.

 

Further Reading

1. Inheritance in Python
2. Polymorphism in Python
3. Encapsulation in Python