How to create Python classes and objects

Python classes are like con­struc­tion plans or templates. You can use them to write reusable code in the form of class at­trib­utes and methods.

What are Python classes?

A class is an abstract concept that outlines at­trib­utes and methods for objects. A Python class acts as a template for creating concrete objects, which are instances of the class. For example, a Car, class could define at­trib­utes like colour and brand, along with methods such as __drive__ or __brake__.

While each object of a class can have unique attribute values, objects of the same class share methods and basic behaviour framework with other instances in the class. For example, the object my_car of the class Car can be created with the colour __red__ and the brand __Toyota__, but the methods __drive__ and __brake__ will auto­mat­ic­ally be trans­ferred to the instance.

How to create Python classes

In Python, you define classes using the keyword class.

class MyClass:
    # Constructor method called when creating an object
    def __init__(self, attribute1, attribute2):
        self.attribute1 = attribute1
        self.attribute2 = attribute2
    
    # Method defined within the class
    def my_method(self):
        return f"Attribute 1: {self.attribute1}, Attribute 2: {self.attribute2}"

The code above defines a class named MyClass. It has a con­struct­or __init__, which is invoked upon object creation, ini­tial­ising two at­trib­utes: attribute1 and attribute2. The my_method method returns a formatted string con­tain­ing the values of these at­trib­utes.

To derive an object from this class, use the class name followed by brackets:

object1 = MyClass("Value 1", "Value 2")
# Calling a method of the object
result = object1.my_method()

Examples of how to use Python classes

Python classes can create complex systems and re­la­tion­ships between different entities. In the following sections, we’ll show you how to work with Python classes.

__str()__ function

The __str__() function in Python is a special method that you can define within Python classes. When im­ple­men­ted, it returns a string that rep­res­ents a user-friendly rep­res­ent­a­tion of an object. You can use the str() function directly on an object or combine it with a print() statement.

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def __str__(self):
        return f"Name: {self.name}, Age: {self.age}"
person1 = Person("Alice", 30)
print(person1) # Output: Name: Alice, Age: 30

In the code above, the __str__() method within the Person class creates a formatted string dis­play­ing a person’s name and age. When print(person1) is executed, it auto­mat­ic­ally calls the __str__() method of the person1 object and outputs the string that is returned by the method.

Defining methods in Python classes

In Python, you can define methods within a class to perform op­er­a­tions on the objects of the class. These methods can then be called by the objects that are created.

class Rectangle:
    def __init__(self, length, width):
        self.length = length
        self.width = width
    
    def area(self):
        return self.length * self.width
    def perimeter(self):
        return 2 * (self.length + self.width)
# Creating an object of the class
my_rectangle = Rectangle(5, 10)
# Calling methods of the object
area = my_rectangle.area()
perimeter = my_rectangle.perimeter()
# Printing the calculated values
print("Area =", area) # Output: Area = 50
print("Perimeter =", perimeter) # Output: Perimeter = 30

In the Python example, we define the class Rectangle with two methods area() and perimeter(), which calculate the rectangle’s area and perimeter using the length and width provided during object ini­tial­isa­tion. In Python, self in a class method acts as a reference to the object, which the method is currently being applied to.

The object my_rectangle is created with a length of 5 and a width of 10. We then call the methods area() and perimeter() on this object to calculate the cor­res­pond­ing values.

Changing the prop­er­ties of objects

The . dot operator can be used to access the specific at­trib­utes of the object and update their values. You can assign new values directly to the attribute.

person1.name = "Sarah"
person1.age = 35

The keyword del is used to delete the prop­er­ties of an object.

del person1.name