Understanding Python Classes, Objects, and Inheritance

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One of the essential concepts in object-oriented programming in Python is classes and objects. This article will provide an overview of these concepts, along with inheritance, their creation, and usage through an extended class example.

Table of Contents

Python Classes

A class is a template or design for multiple objects that share similar characteristics and behaviors. It consists of data attributes (variables) and methods (functions). Use the `class’ keyword followed by the name of the class and its indented contents to create a class in Python:


class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email

In this example, we have created a User class with two attributes (name and email) initialized in the __init__() method, also known as the constructor.

Python Objects

An object is an instance of a class. It is created by calling the class name using parentheses and passing arguments to its constructor:


michael_monroe = User("Michael Monroe", "michael.monroe@example.com")
print(f"Name: {michael_monroe.name}, Email: {michael_monroe.email}")

In this example, we have created an object michael_monroe of the User class and accessed its attributes using dot notation (.).

Class Methods

A method is a function defined within a class that operates on the class’s objects. It can access and modify the data attributes of the object it is called upon:


class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email
    
    def say_hello(self):
        print(f"Hello, {self.name}!")

In this example, we have added a say_hello() method to our User class that prints a greeting using the object’s name attribute.

Inheritance

Inheritance allows us to create new classes based on existing ones, inheriting their attributes and methods. This is achieved by using the keyword `class’ followed by the name of the class with a colon and the name of the parent class in brackets:


class Customer(User):
    def __init__(self, name, email):
        super().__init__(name, email)
        self.is_customer = True

In this example, we have created a Customer class that inherits from the User class. The super() function calls the parent class’s constructor to initialize its attributes.

Extended Class Example

Let’s create an extended customer class with a calculation function for customer turnover:


class Customer(User):
    def __init__(self, name, email):
        super().__init__(name, email)
        self.is_customer = True
        self.purchases = []
    
    def add_purchase(self, product, price):
        self.purchases.append((product, price))
    
    def get_total_spent(self):
        total = sum([price for _, price in self.purchases])
        return f"{self.name} has spent {total:,.2f}"
    
sarah_mueller = Customer("Sarah Mueller", "sarah.mueller@example.com")

sarah_mueller.add_purchase("T-Shirt", 20)
sarah_mueller.add_purchase("Jean", 80)

print(f"Name: {sarah_mueller.name}, Total Spent: {sarah_mueller.get_total_spent()}")

This example adds a purchases list attribute and an add_purchase() method to our base User class. We have also added a get_total_spent() method that calculates the total spent by the customer. The Customer class inherits from this extended User class.

In conclusion, Python classes and objects provide an effective way of organizing code in object-oriented programming. Inheritance allows for reusability and flexibility when creating new classes based on existing ones. By understanding these concepts and their creation and usage, developers can create more maintainable and scalable applications using Python.

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