What are Magic Methods in Python Classes? (45/100 Days of Python)

Day 45 of the “100 Days of Python” blog post series covering magic methods in classes

Python allows developers to create custom classes. In addition to the standard methods and attributes, Python classes also provide a set of special methods known as “magic methods” or “dunder methods” (short for “double underscore methods”). These methods are used to control the behavior of the class and its objects, and they can be used to define custom operations for the class, such as addition, comparison, and iteration.

Magic Methods Overview

Magic methods in Python classes are denoted by a double underscore prefix and a double underscore suffix. For example, the method for defining the behavior of the + operator is called __add__. The magic methods are called automatically by the Python interpreter when a specific operation is performed on an object of the class. Here are some of the most commonly used magic methods in Python classes:

• __init__: This method is called when an object of the class is created. It is used to initialize the attributes of the class.
• __str__: This method is called when the str() function is applied to an object of the class. It is used to return a string representation of the object.
• __len__: This method is called when the len() function is applied to an object of the class. It is used to return the length of the object.
• __add__: This method is called when the + operator is applied to two objects of the class. It is used to define the behavior of the addition operator for the class.
• __eq__: This method is called when the == operator is applied to two objects of the class. It is used to define the behavior of the equality operator for the class.
• __iter__: This method is called when the iter() function is applied to an object of the class. It is used to make the object iterable.

Using Magic Methods in Python Classes

Now that we have a basic understanding of magic methods in Python classes, let’s take a look at how they can be used in practice. Consider the following example where we define a class called Person:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def __str__(self):
        return f'Person(name={self.name}, age={self.age})'

In this example, we have defined two magic methods: __init__ and __str__. The __init__ method is used to initialize the name and age attributes of the class, and the __str__ method is used to return a string representation of the object. Let’s create an object of the Person class and see how it behaves:

person = Person('John Doe', 30)
print(person)
# Person(name=John Doe, age=30)

As you can see, the __str__ method is automatically called when we print the person object, and it returns the string representation of the object.

Let’s take another example where we define a custom class that implements the addition operator:

class Vector:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __str__(self):
        return f'Vector({self.x}, {self.y})'

    def __add__(self, other):
        x = self.x + other.x
        y = self.y + other.y
        return Vector(x, y)

In this example, we have defined a class called Vector that represents a two-dimensional vector. The __init__ method is used to initialize the x and y attributes of the vector, the __str__ method is used to return a string representation of the vector, and the __add__ method is used to define the behavior of the addition operator for the class. Let’s create two vectors and add them:

vector1 = Vector(1, 2)
vector2 = Vector(3, 4)
vector3 = vector1 + vector2
print(vector3)   # Vector(4, 6)

As you can see, the __add__ method is automatically called when we add two vectors, and it returns a new vector that is the sum of the two vectors.

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