Method Overriding in Python: What is it, How to do it?

Python is a high-level, general-purpose language that is a must-learn for computer programming enthusiasts. Similar to other widely-used computer languages like JAVA, C++, Golang, Ruby, etc. Python is also an object-oriented programming language where coding is dependent on classes and objects. The concept allows developers to structure simple, reusable codes which then denote individual objects. There are several useful features that OOP languages offer, one of which is Method Overriding.

In this article, we will understand the concept of inheritance to explore method overriding in Python. Let’s begin with understanding what a class is.

What is a Class?

Class is a feature or instance in the Object-Oriented programming paradigm. It is an extended program coding template within a program. Classes help programmers input the initial data of each object (arrays, strings, variables, etc.) at the time of creation. They also enable us to define the characteristics of the class and determine how they will process data or provide input. There are sub-classes or child-classes under the defined parent-classes or superclasses in a program.

What is Inheritance? What are its benefits?

Inheritance in object-oriented programming is a property that allows a class’s features to be inherited to other classes or subclasses. This helps prevent data redundancy, compile the program better, and limit the scope of making mistakes. 

This capability of a class to derive or inherit features from other classes is known as inheritance. The class whose characteristics and properties are used to derive a subclass is called the Parent class.

Here are the benefits of inheritance: 

• Inheritance allows users to represent real-time relationships well. 
• It allows codes to be reused. It also allows programmers to provide more characteristics to a class.
• It allows for transition. Suppose the class Q derives the features from class W, then the sub-classes of Q would automatically inherit from class W.

Types of Inheritance

There are three types of inheritances which are as follows;

1. Single Inheritance

In single inheritance, a derived class can inherit features from a single parent class. It enables codes to be reused and also the adding of new features.

2. Multiple Inheritance

It refers to transferring the characteristics of more than one parent class to a subclass. Here, the features of the base class are inherited into the sub-class automatically.

3. Multilevel inheritance

When the features of the parent class and the sub-class are further inherited into another derived class, it is called multilevel inheritance.

What is Method Overriding in Python?

Method overriding is a feature of object-oriented programming languages where the subclass or child class can provide the program with specific characteristics or a specific implementation process of data provided that are already defined in the parent class or superclass.

When the same returns, parameters, or name is input in the subclass as in the parent class, then the method of implementation in the subclass overrides the method as mentioned in the parent class. This is known as method overriding.

Its execution depends on the data that is used to invoke the method and not the reference data already provided in the parent class. If an object of the parent class is used to invoke the method of implementation that is specific to a program, then the version of the method as written in the parent class is invoked. On the other hand, if an object of the subclass is used to invoke the method, the execution will be according to the features mentioned in the subclass. If you are a beginner and would like to gain expertise in data science, check out our data science courses.

Overriding is a vital concept of OOP because it allows inheritance to use its full power. With the help of method overriding, a class can copy another class, preventing duplicated code to improve or customise a part of it simultaneously. Thus, method overriding is a part of the inheritance process.

In method overriding, you need to use several methods, with the number of arguments being the same. Now you may be confused about how all these methods are different, although their signatures and names are the same. Well, they differ in location. Methods will be located in different classes.

Let’s understand what is overriding in Python in detail with an example. Suppose you have the function to calculate the employees’ salary hikes in an organisation. However, specific departments’ employees receive salary hikes in different percentages. In that case, you can override the existing method in the ‘Department’ class and then write your logic.

 If you want to override a method in Python, certain conditions must be fulfilled; they are:

• Overriding a method in the same class is not allowed. So, you need to do that in the child class by implementing the Inheritance concept.
• If you want to override the Parent Class method, create a function in the Child with the same name and number of parameters. This is called function overriding in Python.

When does Method overriding occur in Python?

Method overriding comes into the picture when the child class offers the exact implementation of the method provided by the parent class. When a method with identical names and arguments is used in both a base/superclass and a derived class, the derived class method overrides the method available in the base class.

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Features of Method Overriding

This section is going to explore the salient features that method overriding in python offers:

• Method overriding allows the usage of functions and methods in Python that have the same name or signature.
• Method overloading is an example of runtime polymorphism.
• In method overriding, using the feature of inheritance is always required.
• Method overloading is carried out between parent classes and child classes.
• It is used to change the behaviour and implementation of existing methods.
• There is always a need for a minimum of two classes for method overriding.

Use Of Method Overriding In Python For Data Science:

To understand what is overriding in Python, you must also know how it is used in data science. Method overriding allows you to redefine a method in a subclass or the derived class previously defined in its parent or the superclass. An OOP language can allow a child class or subclass to have a customised implementation of a method already provided by one of its parent classes or super-classes.

The function overriding in Python is used for runtime polymorphism. Remember that the method’s name should be the same as the parent class’s method. Moreover, method overriding is only possible in an OOP language when two classes have an identical ‘Is-a’ inheritance connection. Also, the parameter included in the method should be identical to those in the parent class. When going through the features of overriding and overloading in Python, you should know how they are used in data science.

Benefits of Method Overriding in Python:

Both overriding and overloading in Python provide unique benefits. Let’s go through the benefits of method overriding in python.

• Overriding methods permit a user to change the existing methods’ behaviour. For its implementation, a minimum of two classes are needed.
• The key benefit is that it allows the main class to declare those methods shared by all. Also, it allows subclasses to define their implementations of any or all such methods.
• When overriding a method, you need to use inheritance.
• The parent class function and child class function must have the same signature. They must have the same number of parameters.
• It allows a child class to adapt the execution of any method provided by any one of its parent classes.

Difference Between Method Overloading And Method Overriding In Python

•  Implementation:

The method overloading and method overriding in Python largely differ based on how they are implemented. Method overloading is implemented to get an improved definition of methods as per various situations. On the other hand, method overriding provides a precise implementation of methods that are defined in the parent class.

Method Overloading is implemented in a single class in which one class has unique definitions of a method. On the other hand, method overriding takes place between two classes with an IS-A (Inheritance) relationship among them.

• Time of implementation:

The method overloading and overriding in Python also differ based on implementation time. Method Overloading occurs at compile time; therefore, it is called Compile time Polymorphism. Method Overriding occurs at runtime; therefore, it is called runtime Polymorphism.

•  Syntax:

When considering the difference between method overloading and method overriding in Python, you must know how they are defined. In method overloading, parameter ordering, parameter count, and data type differ. In method overriding, all these are the same.

Return type:

You must understand the return type when deciding which one to choose from method overloading and overriding in Python. The method’s return type can be the same or different in method overloading. But in method overriding, the method’s return type must be the same in both the child class and parent class.

•  Static method:

You can overload static methods, which means there can be unique static methods overloaded in the same class. But static methods are never overridden, so a static method in a base class and parent class are unrelated.

•  Private and final methods:

Both the private and final methods can be overloaded in a class. So, a class can have overloaded with more than one private and final method. But the private and final methods are never overridden in a child class.

Understanding Method Overriding: Multiple and Multilevel Inheritance

Multiple and multilevel inheritances are two types of inheritances offered by most object-oriented programming languages. In this section, we will see how method overriding is used in various and multilevel inheritances:

Inheritance is inevitable in method overriding as it connects the parent class (superclass) and the child class methods. When an overridden method is called, the derived class’s method is also invoked. So, the method used in the base class now becomes hidden. As the name suggests, inheritance allows one class to inherit another class’ properties. One of the differences between overloading and overriding in Python is that overloading doesn’t use inheritance.

Now let’s understand inheritance with a practical example:

Son inherits all features from his Father; however, he has unique features too. The Father is the parent class (also known as a super class or base class), and the Son is the child class (also known as a derived class).

Now we know how inheritance works, let’s understand what happens during method overriding implementation.

Class2 (Son class) inherits Class1 (Father class). The Son class’ object can access the Father class’ method. Moreover, it accesses its own methods. However, because the method names are identical in both these classes, the child class’ method overrides the parent class’ method.

1. Multiple Inheritance

In this kind of inheritance of class or object, a subclass inherits features and characteristics of multiple parent classes or bases. For example, there are three different parent classes- class.1, class.2, class.3, and there is class.a, which is the child class executing features of multiple inheritances. The class.a will contain features inherited from all three base classes.

Here is a sample program:

# Defining parent class 1 

class Parent1(): 

    # Parent’s show method 

    def show(self): 

        print(“Inside Parent1”) 

# Defining Parent class 2 

class Parent2(): 

    # Parent’s show method 

    def display(self): 

        print(“Inside Parent2”) 

# Defining child class 

class Child(Parent1, Parent2): 

    # Child’s show method 

    def show(self): 

        print(“Inside Child”)   

# Driver’s code 

obj = Child() 

obj.show() 

obj.display()

Output:

Inside Child

Inside Parent2

2. Multilevel Inheritance

In this kind of inheritance of class or object, a subclass is directly inherited from the base class, already bearing characteristics of the parent class. It is basically like the father-son or grandfather-grandchild relationship. The features of the subclass are unique to its parent class. For example, there is a parent class named class.Q, and a subclass is formed in the extension of the class.Q. Here, the sub-class can act as the base class for another sub-class.

Here is a sample program:

class Parent():  

    def display(self): 

        print(“Inside Parent”) 

class Child(Parent): 

    # Child’s show method 

    def show(self): 

        print(“Inside Child”) 

class GrandChild(Child):  

    # Child’s show method 

    def show(self): 

        print(“Inside GrandChild”)          

# Driver code  

g = GrandChild()    

g.show() 

g.display()

Output:

Inside GrandChild

Inside Parent

Invocation of Base Class Methods within Overridden Methods

There is a method where parent class methods can be invoked in between overridden methods. It can be done by using the following processes:

•  Using class name

writing class name method in the overridden method in the subclass can invoke the method provided in the parent class.

• Using the function of super()

the programming language of Python offers a function called super(), which is used to refer to the parent class especially.

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Conclusion

Method overriding is one of the most crucial features of the Python language. The property finds extensive use in programming data science applications and allows for compact and efficient data analysis. Method overriding also makes the compilation of codes and rechecking easier. There are some prerequisites to using this feature: understanding the basic concept of classes and inheritance. 

If you’d like to learn in-depth about method overriding in Python, we suggest you take up the 18-month Master of Science in Data Science. upGrad offers this course from IIIT Bangalore and Liverpool John Moore’s University. The course teaches you skills like Statistics, Predictive Analytics using Python, Machine Learning, Data Visualization, Big Data Analytics, and more. Students with a strong knowledge of concepts of Python are well-positioned to tackle subjects like Deep Learning, Natural Language Processing, Business Analytics, and Data Engineering. 

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