Understanding Python Inheritance: A Comprehensive Guide

Inheritance in Python is a foundational concept in object-oriented programming. It allows a class, referred to as the child class, to inherit attributes and behaviors (methods and properties) from another class, known as the parent class. This technique enhances code reusability and logical hierarchy.

Defining a Parent Class

In Python, any class can serve as a parent class. The syntax is straightforward and identical to creating a regular class. Below is an example where we define a class named Person with two attributes, firstname and lastname, along with a method to print the full name.

class Person:
  def __init__(self, fname, lname):
    self.firstname = fname
    self.lastname = lname

  def printname(self):
    print(self.firstname, self.lastname)

# Creating an object of the Person class
x = Person("John", "Doe")
x.printname()

Creating a Child Class

To implement inheritance, define a new class that references the parent class within its declaration. In the following example, the Student class inherits from the Person class:

class Student(Person):
  pass

# Using the Student class
x = Student("Mike", "Olsen")
x.printname()

The keyword pass is used as a placeholder when no additional attributes or methods are defined initially.

Customizing the Child Class with __init__()

While the child class automatically inherits the __init__() method from the parent, you can override it to introduce new attributes. However, doing so requires explicitly calling the parent’s constructor to retain inherited properties.

class Student(Person):
  def __init__(self, fname, lname):
    Person.__init__(self, fname, lname)

Alternatively, Python provides the super() function for a cleaner and more modern approach:

class Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)

Adding New Properties

You can enhance the child class by adding new attributes. For example, let’s add a graduationyear property and make it dynamic by passing it as a parameter during object creation:

class Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.graduationyear = year

x = Student("Mike", "Olsen", 2019)

Introducing Additional Methods

To expand the functionality of the child class, define custom methods. Below, the welcome() method greets the student and references their graduation year:

class Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.graduationyear = year

  def welcome(self):
    print("Welcome", self.firstname, self.lastname, "to the class of", self.graduationyear)

Conclusion

Mastering inheritance in Python equips developers with the tools to write clean, modular, and reusable code. By understanding how to define and extend classes using built-in features like super(), you can build robust and scalable applications with greater ease. For more programming tutorials, explore additional Python resources at Devyra.