Inheritance in Python With Examples

In this tutorial you’ll learn about OOPS concept inheritance and how to use inheritance in Python.

Inheritance concept

Inheritance allows us to create a class that acquires, all the properties and methods of another class.

The class whose members are inherited is called the Super class. Also known as parent class or base class.

The class that inherits from another class is called the Sub class. Also known as child class or derived class.

Python inheritance syntax

If there is a class called ParentClass defined as-

class ParentClass:
  body of parent class

Then a ChildClass that inherits from this ParentClass can be defined as-

class ChildClass(ParentClass):
  body of child class

Inheritance Python example

In the example there is a class called Person that acts as a base class and another class Employee that inherits from Person class.

class Person:
  def __init__(self, name, age):
    self.name = name
    self.age = age

  def display_person(self):
    print('In display_person method')
    print('Name:', self.name)
    print('Age:', self.age)

class Employee(Person):
  pass

e = Employee("Michael Weyman", 42)
e.display_person()

Output

In display_person method
Name: Michael Weyman
Age: 42

As you can see in Employee class just pass keyword is used to specify that it doesn’t add any property or method to a class. It just inherits all the properties and methods of the class it inherits from.

You can create an object of Employee class and initialize the ‘name’ and ‘age’ properties because Employee class inherits these properties from Person class. Same way you can also call the method display_person() method using the object of Employee class.

Constructor overriding and use of super with inheritance

When a class inherits another class in Python, by default constructor of the super class is also available to the child class. If you have extra fields in the child class which you need to initialize in the child class then you can override the constructor in the child class to initialize the fields there.

In most of the scenarios you’ll inherit from a base class and add properties and methods of its own in the child class as well. To initialize the properties of the child class you can add __init__() function in the child class too. In our Employee class let’s add two fields person_id and department and add a method display_employee() too.

class Employee(Person):
  def __init__(self, person_id, department, name, age):
    self.name = name
    self.age = age
    self.person_id = person_id
    self.department = department

  def display_employee(self):
    print('In display_employee method')
    print('Id:', self.person_id)
    print('Name:', self.name)
    print('Age:', self.age)
    print('Department:', self.department)

In the above class you can notice the redundancy of initializing the parent class’ fields in the constructor though there is a constructor in the parent class which is already doing that. Same way in the display_employee () method we have print statements to print name and age too though there is a method in Person class which is already doing that.

If you want to call super class constructor and methods from sub-class that can be done using super() function which helps in avoiding code redundancy as present in the above Employee class. Here is the modified Employee class with usage of super() function.

class Employee(Person):
  def __init__(self, person_id, department, name, age):
    # call constructor of super class
    super().__init__(name, age)
    self.person_id = person_id
    self.department = department

  def display_employee(self):
    # call method of super class
    super().display_person()
    print('In display_employee method')
    print('Id:', self.person_id)
    print('Department:', self.department)

e = Employee(1, "IT", "Michael Weyman", 42)
e.display_employee()

Output

In display_person method
Name: Michael Weyman
Age: 42
In display_employee method
Id: 1
Department: IT

Advantages of inheritance

Inheritance helps in writing reusable code where you can use the existing functionality just by inheriting from an existing class.
Inheritance helps in writing hierarchical code where you write more generalized code in the super class and then move on to inherit it and add more specific methods. For example you can have a Vehicle super class with more generic functionality like accelerate(), brake(), gear(). Then inherit it to create more specialized classes like Car, Bus, MotorCycle and further down to inherit from Car to create more specific classes like SUV, SportsCar.
Also makes managing the code easy because you don’t put all the functionality in the same class you rather create several classes to create a hierarchical structure with code distributed among those classes.

That's all for the topic Inheritance in Python With Examples. If something is missing or you have something to share about the topic please write a comment.

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January 11, 2021