Operator Overloading & Dunder Methods

NITIN GUPTA

 Operator overloading and Dunder Methods may be new concepts for some of you. However, we have already seen similar concepts in which different methods act differently on different occasions and places. Let us understand the Operator overloading first.

Operator Overloading In Python

Operator overloading means giving new meanings to an operator. In simple words, it means to assign new functionality to an operator beyond its normal functioning. We will go with the most common and easiest that we could find related to the concept, i.e., the + sign. For numbers, it is used for addition between them, but in the case of a string, it is used to join or combine two strings, working differently in two different scenarios. The operators are methods defined in respective classes. Defining methods for operators is known as operator overloading.

Python Dunder Methods Or Special Functions

Dunder methods in Python are special methods. In Python, we sometimes see method names with a double underscore (__), such as the __init__ method that every class has. These methods are called “dunder” methods. In Python, Dunder methods are used for operator overloading and customizing some other function’s behavior.

Python usually calls dunder methods under the hood. Suppose we want to join a string with a number using the + sign. Now joining between two different data types is not possible in Python, and the resultant in such a case will be an error. So for this purpose, we can use a function provided to us by Python, named as dunder function. We will write such code in it so that it may first convert the number to a string and then join them, or any other logic will be fine too until it does what we require. We can even return 85; regardless of what string or number is given to us, it is all up to us. 

Methods starting with a double underscore ( __ ) and ending with a double underscore ( __ ) represent dunder methods.

Check https://docs.python.org/2/library/operator.html to explore more about operator overloading.

__str__ and __repr__ functions

Both of these built-in methods are used to return a presentable description of any object rather than the default one. The difference in them is the way of writing them. The __str__ method is mainly written for the end-user, while __repr__ is written for a developer. It is overridden to return a printable string representation of any user-defined class. An interesting thing to note here is that the priority of __str__ is greater than __repr__. This means that if we pass an object into a print statement, it will return us the __str__ string even if __repr__ is also present there. In such cases, if we want to print __repr__, we have to call it exclusively with the object name in the print statement.

Difference between __str__ and __repr__ functions

  1. If the implementation of __str__ is missing, then __repr__ function is used as a fallback. If the implementation of __repr__ is missing, then there will be no fallback.
  2. If __repr__ function is returning the object's String representation, we can skip the implementation of __str__ function. 
  3. The priority of __str__ is higher than __repr__.

Code as described/written in the video

class Employee:
    no_of_leaves = 8

    def __init__(self, aname, asalary, arole):
        self.name = aname
        self.salary = asalary
        self.role = arole

    def printdetails(self):
        return f"The Name is {self.name}. Salary is {self.salary} and role is {self.role}"

    @classmethod
    def change_leaves(cls, newleaves):
        cls.no_of_leaves = newleaves

    def __add__(self, other):
        return self.salary + other.salary

    def __truediv__(self, other):
        return self.salary / other.salary

    def __repr__(self):
        return f"Employee('{self.name}', {self.salary}, '{self.role}')"

    def __str__(self):
        return f"The Name is {self.name}. Salary is {self.salary} and role is {self.role}"

emp1 =Employee("Harry", 345, "Programmer")
# emp2 =Employee("Rohan", 55, "Cleaner")
print(str(emp1))

Comments

Post a Comment

Popular posts from this blog

HOW IMPORT WORKS IN PYTHON?

NITIN GUPTA
  How does the import keyword work? When we write a certain module name along with the  import  keyword, it will start searching for a file with that name having an extension  .py . After finding the file, it will import it into our program, which means that it will permit our program to use the functions of the certain module we imported. We can import a module named  “sys”  to see the path that our import statement takes while searching for a module. import sys print ( sys . path ) Copy sys.path  prints out a list of directories. When we tell Python to import something, then it looks in each of the listed locations in order.  A common mistake that most of the beginners do and also the primary reason for making this tutorial is, why can’t we name our file, the same as the name of a module. The reason is associated with the path. When we give our file a name same as the name of a module, then instead of importing the original module, the system ...
Read more

Exercise 5: Health Management System

NITIN GUPTA
  Exercise#5 The task is to create a " Health Management System ." Suppose you are a fitness trainer and nutritionist. You have to deal with three clients, i.e., (Harry, Rohan, Hammad). For each client, you have to design their exercise and diet plan. Instructions: Create a food log file for each client Create an exercise log file for each client. Ask the user whether they want to log or retrieve client data. Write a function that takes the user input of the client's name. After the client's name is entered, it will display a message as "What you want to log- Diet or Exercise". Use function def getdate ( ) : import datetime return datetime . datetime . now ( ) Copy The purpose of this function is to give time with every record of food or exercise added in the file. Write a function to retrieve exercise or food file records for any client. You are advised to participate in solving this problem. This task helps you to become a good pr...
Read more

*args and **kwargs In Python

NITIN GUPTA
  Before discussing *args and **kwargs, we should have a basic knowledge about types of arguments. In Python programming, there are two types of arguments that can be passed in a function. positional arguments keyword arguments Positional arguments  are the one in which an order has to be followed while passing arguments. We have been dealing with them until now. We know how normal functions work with positional arguments, so now we will directly start exploring keyword arguments. But to understand them, we have to know about asterisk or more commonly known in Perl 6 and ruby as a splat operator.  Asterisk is used in python as a mathematical symbol for multiplication, but in case of arguments, it refers to unpacking. The unpacking could be for a list, tuple, or a dictionary. We will discover more about it by defining *args and **kwargs. *args: args is a short form used for arguments. It is used to unpack an argument. In the case of *args, the argument could be a list or t...
Read more