Understanding Classes in Python: Everything About Classes and Attributes

1. What is a Class in Python?

In Python, a class is a blueprint or a template for creating objects that have similar characteristics and behaviors. It provides a structure for organizing and grouping data and functions that operate on that data. In this tutorial, we'll go over the basics of defining and using classes in Python.

1.1. Defining a Class

To define a class in Python, you use the class keyword, followed by the name of the class. Here is a simple example:

python
class Person:
    pass

This creates a new class called Person that doesn't do anything. The pass statement is used as a placeholder for future code.

2. Class Attributes

A class can have attributes that are shared by all instances of the class. To define a class attribute, you simply create a variable inside the class:

python
class Person:
    species = 'human'

In this case, species is a class attribute that is shared by all instances of the Person class. You can access this attribute using the class name:

python
print(Person.species) # Output: 'human'

3. Class Methods

A class can also have methods, which are functions that are associated with the class. These methods can access and modify the class attributes and can be used to perform operations on instances of the class. To define a class method, you use the def keyword inside the class:

python
class Person:
    species = 'human'
    
    def greet(self):
        print('Hello, I am a', self.species)

In this example, greet() is a class method that takes one parameter (self), which refers to the instance of the class. The method simply prints a greeting that includes the species the attribute of the class.

To use the class method, you create an instance of the class and call the method on that instance:

python
person = Person()
person.greet() # Output: 'Hello, I am a human'

4. Instance Attributes

In addition to class attributes, each instance of a class can have its own attributes that are specific to that instance. To define an instance attribute, you create a variable inside the __init__() method of the class:

python
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age
        
    def introduce(self):
        print('My name is', self.name, 'and I am', self.age, 'years old.')

In this example, the __init__() the method is used to initialize the name and age attributes of the instance. These attributes are specific to each instance of the Person class. The introduce() the method is used to print out the name and age of the instance.

To create an instance of the class, you simply call the class name with any required parameters:

python
person = Person('Alice', 25)
person.introduce() # Output: 'My name is Alice and I am 25 years old.'

5. Private Attributes

Private attributes are attributes that are intended to be used only within the class. They are prefixed with double underscores __ to make them private. Private attributes can only be accessed within the class using the same name or through instance methods defined within the class. They cannot be accessed directly from outside the class or even from subclasses.

Here's an example class that demonstrates private attributes:

python
class MyClass:
    def __init__(self, public_attribute, private_attribute):
        self.public_attribute = public_attribute
        self.__private_attribute = private_attribute
    
    def get_private_attribute(self):
        return self.__private_attribute
    
    def set_private_attribute(self, value):
        self.__private_attribute = value
    
    def print_attributes(self):
        print(f'Public attribute: {self.public_attribute}')
        print(f'Private attribute: {self.__private_attribute}')

In this example, we define a class MyClass with a public attribute public_attribute and a private attribute __private_attribute. We also define instance methods get_private_attribute() and set_private_attribute() to get and set the value of the private attribute, respectively. The method print_attributes() is defined to print both the public and private attributes.

python
obj = MyClass('public', 'private')
print(obj.public_attribute)             # Output: public

# This will raise an AttributeError because the attribute is private.
print(obj.__private_attribute)

print(obj.get_private_attribute())      # Output: private

obj.set_private_attribute('new value')
print(obj.get_private_attribute())      # Output: new value

obj.print_attributes()
# Output: Public attribute: public
#         Private attribute: new value

In this example, we can access the public attribute public_attribute directly using the instance name. However, we cannot access the private attribute __private_attribute directly from outside the class. We can only access it using the instance methods get_private_attribute() and set_private_attribute(). When we call the print_attributes() method, we can see that both the public and private attributes are printed.

Note that although private attributes cannot be accessed directly from outside the class, they can still be accessed using the _ClassName__private_attribute syntax. However, this is considered bad practice and should be avoided.

6. Example Class that demonstrates each type of attribute:

python
class MyClass:
    class_attribute = 'class attribute'
    
    def __init__(self, instance_attribute):
        self.instance_attribute = instance_attribute
    
    def instance_method(self):
        print('This is an instance method.')
    
    @classmethod
    def class_method(cls):
        print('This is a class method.')
    
    @staticmethod
    def static_method():
        print('This is a static method.')

In this example, we define a class MyClass with a class attribute class_attribute, an instance attribute instance_attribute, an instance method instance_method(), a class method class_method(), and a static method static_method(). Here's how we can access each of these attributes:

python
print(MyClass.class_attribute)     # Output: class attribute

obj = MyClass('instance attribute')
print(obj.instance_attribute)      # Output: instance attribute

obj.instance_method()             # Output: This is an instance method.
MyClass.class_method()            # Output: This is a class method.
MyClass.static_method()           # Output: This is a static method.

In this example, class_attribute is a class attribute that is shared by all instances of the class. instance_attribute is an instance attribute that is specific to each instance of the class. instance_method() is an instance method that can only be called on instances of the class. class_method() is a class method that can be called on the class itself, and static_method() is a static method that can also be called on the class itself.


2. Types of Classes in Python

In Python, there are several types of classes that you can define, depending on your requirements. Here are the most common types of classes in Python:

  1. Simple Class:

A simple class is the most basic type of class in Python. It defines attributes and methods, which can be used to represent an object. Here's an example of a simple class:

python
class Dog:
    def __init__(self, name, breed):
        self.name = name
        self.breed = breed
        
    def bark(self):
        print(f'{self.name} barks!')

In this example, we define a Dog class with two attributes, name and breed, and one method, bark(). The __init__() method is used to initialize the name and breed attributes with the values passed as arguments. The bark() method simply prints a message indicating that the dog is barking.


  1. Abstract Class:

An abstract class is a class that cannot be instantiated directly but can be used as a base class for other classes. It defines abstract methods that must be implemented in any concrete subclass. Here's an example of an abstract class:

python
from abc import ABC, abstractmethod

class Animal(ABC):
    @abstractmethod
    def make_sound(self):
        pass
        
class Dog(Animal):
    def make_sound(self):
        print('Woof!')

In this example, we define an abstract class Animal that has one abstract method, make_sound(). The @abstractmethod decorator is used to indicating that this method must be implemented in any concrete subclass. We define a concrete subclass Dog that implements the make_sound() method by printing 'Woof!' to the console.


  1. Concrete Class:

A concrete class is a class that can be instantiated and used directly. It doesn't have any abstract methods that need to be implemented in any subclass. Here's an example of a concrete class:

python
class Car:
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year
        
    def start_engine(self):
        print(f'{self.make} {self.model} ({self.year}) engine started!')

In this example, we define a Car class with three attributes, make, model, and year, and one method, start_engine(). The __init__() method is used to initialize the attributes with the values passed as arguments. The start_engine() method simply prints a message indicating that the car's engine has been started.


  1. Inherited Class:

An inherited class is a class that inherits attributes and methods from a parent class. It can add new attributes and methods, or override existing ones. Here's an example of an inherited class:

python
class Animal:
    def __init__(self, name):
        self.name = name
        
    def make_sound(self):
        print('Animal makes sound!')
        
class Dog(Animal):
    def make_sound(self):
        print('Woof!')

In this example, we define a Animal class with one attribute, name, and one method, make_sound(). We define a Dog class that inherits from Animal and overrides the make_sound() method with its own implementation. When make_sound() is called on an instance of Dog, it prints 'Woof!' to the console.


  1. Mixin Class:

A mixin class is a class that provides specific functionality that can be added to other classes. It doesn't have its own instance attributes but defines methods that can be used by other classes. Here's an example of a mixin class:


python
class FlyMixin:
    def fly(self):
        print(f'{self.__class__.__name__} flies!')
        
class Bird(FlyMixin):
    def __init__(self, name):
        self.name = name
        
class Plane(FlyMixin):
    def __init__(self, model):
        self.model = model

In this example, we define a FlyMixin the class that has one method, fly(), which simply prints a message indicating that the object is flying. We define two classes, Bird and Plane, that inherit from FlyMixin and can use the fly() method. The Bird the class has an additional attribute, name, while the Plane the class has an additional attribute, model.


  1. Metaclass:

A metaclass is a class that defines the behavior of other classes. It's used to customize the behavior of class creation and class instances. Here's an example of a metaclass:

python
class MyMeta(type):
    def __new__(cls, name, bases, attrs):
        attrs['class_name'] = name
        return super().__new__(cls, name, bases, attrs)
        
class MyClass(metaclass=MyMeta):
    pass

In this example, we define a metaclass MyMeta that has a __new__() method. This method is called when a new class is created, and it adds a new attribute, class_name, to the class. We define a MyClass class that uses MyMeta as its metaclass, which means that MyMeta's __new__() method is called when MyClass is created. When we create an instance of MyClass, it has a class_name attribute that is set to 'MyClass'.


  1. Singleton Class:

A singleton class is a class that allows only one instance to be created. This is useful when you want to ensure that there's only one instance of a class in your program. Here's an example of a singleton class:

python
class Singleton:
    _instance = None
    
    def __new__(cls):
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance

In this example, we define a Singleton class that has a private class attribute _instance, which is initially set to None. The __new__() method is used to create a new instance of the class if _instance is None, or return the existing instance if it's not. When we create multiple instances of Singleton, we always get the same instance.


  1. Data Class:

A data class is a class that is designed primarily to store data. It automatically generates special methods such as __init__(), __repr__(), __eq__(), and __hash__(). Here's an example of a data class:

python
from dataclasses import dataclass

@dataclass
class Person:
    name: str
    age: int
    email: str

In this example, we define a Person class using the @dataclass decorator. The class has three attributes, name, age, and email, which are automatically initialized by the __init__() method generated by dataclass. The __repr__(), __eq__(), and __hash__() methods are also automatically generated. We can create instances of Person and access its attributes directly, like this:

python
person = Person('John', 30, '[email protected]')
print(person.name)     # Output: John
print(person.age)      # Output: 30
print(person.email)    # Output: [email protected]

Conclusion

In this tutorial, we've covered the basics of defining and using classes in Python. A class is a blueprint or a template for creating objects that have similar characteristics and behaviors. It provides a structure for organizing and grouping data and functions that operate on that data. We've looked at defining class attributes, class methods, instance attributes, and how to create instances of a class. With this knowledge, you can start building more complex programs using classes and objects.


Author
Vaneesh Behl
Passionately writing and working in Tech Space for more than a decade.

Comments

Post a Comment

Popular posts from this blog

Top 7 Web Development Trends in the Market

Image
  Technology continues to advance as humans discover new methods to innovate, doing tasks quicker and more creatively than before. Developers are continuously on the lookout for new technologies that will help them move forward towards a better future.  The contemporary industry is constantly evolving, and new online technologies emerge daily. Entrepreneurs that want to interact with more consumers and stay ahead in this competitive industry may take advantage of these new trends. There aren't many industries that have as much innovation as bespoke web development. Hire WordPress developer to help entrepreneurs interact with more consumers and stay ahead. Websites, without a question, play an important part in today's commercial environment. A WordPress design agency will build you a website that functions as a separate brand, organization, and individual. Doing business on a worldwide scale has become conceivable and attainable as firms and enterprises have transcended all bou
Read more

What's New in Selenium-Automated Testing

Image
  What's New  in Selenium-Automated Visual Testing   Selenium has been one of the most popular tools for automating cross-browser testing of web applications. Earlier this year, Simon Stewart (the creator of WebDriver and a pivotal contributor to Selenium projects) formally announced Selenium 4. Due to its redesigned features and functionalities, Selenium 4 has gained enormous traction since then. This is one of the critical improvements in Selenium 4 and a new, shiny UI design for a better user experience. In this article, we are going to see what is trending and new testing has come in selenium-automated visual testing.   Table of contents: What is Selenium-automated? Who has developed Selenium? What is Visual testing? How to perform Visual Testing using Selenium? What is new in Selenium-automated? Conclusion What is Selenium-automated:    This tool can be integrated with tools such as TestNG and JUnit for managing test cases and producing reports. It consists of a suite of free
Read more

Automation Practice: Automate Amazon like E-Commerce Website with Selenium

Image
In this post, you will learn to automate different functionalities of an e-commerce website. To automate this practice assignment,  you should have sound knowledge of all the Selenium concepts. We'll create a test plan and then automate an e-commerce website that is quite similar to amazon.com. Automate Amazon-like e-Comm website with Selenium for Automation Practice Table of Content 1. What should you know before starting this Project assignment? 2. Which functionalities will we automate in this Project assignment? 3. Create Test Plan for Amazon like e-commerce website 4. Automate Amazon like e-commerce website: Automate User Registration and Login of e-commerce website Automate Search feature of e-commerce website Automate "Buy Product" feature of e-Commerce website 1. What should you know before automating this automation assignment? You should know the following topics, before starting this project assignment: Software Testing Concept
Read more

Selenium IDE Tutorial: How to Automate Web Testing with Easy-to-Use Interface

Image
1. What is Selenium IDE? Selenium IDE (Integrated Development Environment) is a browser-based tool used for automating web application testing. It is an open-source record-and-playback tool that allows testers and developers to create automated test cases without the need for extensive programming knowledge. Selenium IDE provides a simple and user-friendly interface for creating and executing test cases. It records user interactions with a web application and generates corresponding code in Selenium's scripting language. This makes it easy to create automated tests quickly and efficiently. Table of Contents 1. Introduction to Selenium IDE      1.1 What is Selenium IDE?      1.2 Benefits of Using Selenium IDE      1.3 Features of Selenium IDE      1.4 Difference between Selenium IDE and Webdriver      1.5 Getting Started with Selenium IDE 2. How Selenium IDE Works 3. Recording and Playing Back Test Cases      3.1 Recording Test Cases      3.2 Playing Back Test Cases      3.3 Managin
Read more

Mastering Selenium WebDriver: 25+ Essential Commands for Effective Web Testing

Image
In this tutorial, you will learn about the most important Selenium WebDriver Commands which would be the backbone of your GUI automation scripts.  We have divided the commands in to different categories so that you can learn Selenium commands without difficulty. This Selenium Commands tutorial has explained you all the commands with Code examples and sample Selenium programs for better understanding. Table of Content 1. Selenium Browser Commands 2. Get Commands 3. Navigation Commands 4. Web Element Commands 5. Select Dropdown Commands 1. Selenium Browser Commands Browser commands are the starting point of your Selenium WebDriver script. These commands used to launch browser, maximize it, open URL to be tested and other navigation commands. i. Set Path of browser/driver executable: It is the starting point of the WebDriver script.  You have to download the browser executable file for the browser and make sure it is compatible with the version of your browser. For example, for fir
Read more

What Is Artificial Intelligence (AI) and How Does It Work?

Image
Artificial Intelligence, often abbreviated as AI, is a transformative field of computer science that aims to create machines, software, or systems capable of performing tasks that typically require human intelligence. These tasks include problem-solving, learning from experience, understanding natural language, recognizing patterns, and making decisions. In this article, we will explore what AI is, its subfields, and provide examples of AI applications that have already started to shape our world. Understanding Artificial Intelligence AI is a multidisciplinary field that draws inspiration from various areas, including computer science, mathematics, psychology, neuroscience, and linguistics. At its core, AI seeks to replicate or simulate human intelligence in machines, enabling them to perform tasks autonomously, adapt to changing environments, and improve over time. Subfields of Artificial Intelligence AI encompasses several subfields, each with its unique focus and applications: 1. Ma
Read more

17 Best Demo Websites for Automation Testing Practice

Image
We need demo websites for various purposes, like learning new tools and for automation testing practice. In this post, we cherry-picked some of the best websites to practice Selenium automation testing. This set of demo websites would help you to enhance your automation skills.  This post can help various people like,  Automation Testing learners, Experienced professionals, and even Automation Testing tutors/teachers. They all can benefit from these demo websites. Table of Contents 1. Techlistic Automation Practice Form 2. Amazon like Demo E-Commerce Website 3. Make My Trip like Travel Portal 4. Demo Automation Practice Web Table 5. Google.com 6. Demo Website for Handling Alerts 7. Way2Automation Demo 8. NewTours DemoAUT 9. The Demo Site 10. DemoQA 11. Para Bank 12. Orange HRM 13. Sauce Labs Demo E-Commerce Site 14. Demo Bank Demo Websites for API Automation Testing Practice 15. Restful Booker 16. Pet Store 17. Demo REST API Best Demo Websites for Automation Practice Let's take
Read more

What is Java Class and Object?

Image
In this Java Class and Object tutorial, we will learn about the fundamentals of Java Programming. Java Class and Object are the base of Java. And we have tried to explain it in a simpler way. For your better understanding, we have also provided example Java programs for concepts of Java Classes and Object and Java Constructors. Classes and Objects are the fundamental building blocks of OOPS (Object Oriented Programming). A Java object is a physical and logical entity whereas a Java class is a logical entity. Table of Content 1. What is a Java Class? Syntax of java Class Explanation of example code Types Of Java Classes 2. What is a Java Object? How to create Java Object? Example Code and it's explanation What is the use of Java Objects? 3. Write your first Java Program - "Hello World" 4. What is Java Constructor? Non-Parameterized Constructor (Default) Parameterized Constructor 1. What is a Java Class? Before creating an object in Java, you need to define a class. A class
Read more

Java Date Format Validation with Regular Expressions: A Step-by-Step Guide

Image
1. Introduction Validating date formats is an essential aspect of many software applications. It ensures that the user inputs a date in the correct format, reducing the risk of errors and inconsistencies in data. Regular expressions are a powerful tool for validating date formats. In this tutorial, we will explore how to validate date formats using regular expressions in Java.
Read more

Find Broken Links on Webpage with Selenium Automation

Image
As an Automation Tester, you get to play with links present on the website. Links are one of the most important parts of the webpage. So, it's always important to not leave any broken links on any website. Testing the links manually could be a tough and time taking task. In this post, we'll learn to automate URL link testing. 1. What is a Broken Link? A broken link is a URL that is not working or not reachable. There are multiple reasons for its dis-functioning. There are different HTTP error status codes that the browser shows when the link is broken. These error codes have different meanings. Let's take a look at the different HTTP status codes. 200 - It means success, the link is working. 404 - It's the most common one, which means Page not found. 403 - Authorization is required to access the page.  400 - It has different meanings, bad request, bad host, timeout, etc. 500 - Internal server error. 2. Why a link broke? A link might not be working due to many reasons,
Read more