Python Basics 10

Introduction to Object-Oriented Programming

Index

1. Introduction to Object-Oriented Programming (OOP)

2. Class and Object

3. Constructors

4. Class, Object, and Instance Attributes

5. Self Parameter

6. Methods in Object

7. Static Method

8. Decorators

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1. Introduction to Object-Oriented Programming (OOP)

Definition:
Object-Oriented Programming (OOP) is a programming paradigm that organizes software design around objects rather than functions and logic. Objects can represent real-world entities with attributes (data) and methods (functions) that operate on the data.

Use-Case Example:
OOP is used to model complex systems where different entities (objects) interact. For instance, an e-commerce system with customers, products, and orders can be modeled using objects.

Key Concepts:

• Class: A blueprint for creating objects.

• Object: An instance of a class.

• Encapsulation: Restricting access to the internal state of an object.

• Inheritance: Creating new classes from existing ones.

• Polymorphism: Using a common interface for different types of objects.

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2. Class and Object

Definition:

• Class: A blueprint or template for creating objects (instances). It defines the attributes and behaviors of the object.

• Object: An instance of a class that holds the actual data and interacts with the class’s methods.

Use-Case Example:
A class Car defines the blueprint for all cars, while each car object (e.g., my_car, your_car) is an instance of the Carclass with specific attributes like color, brand, and model.

Syntax:

class ClassName:
    # Class attributes and methods

# Creating an object
obj = ClassName()

Basic Example:

class Car:
    def __init__(self, brand, model):
        self.brand = brand
        self.model = model

# Creating an object of the Car class
my_car = Car("Toyota", "Corolla")
print(my_car.brand, my_car.model)  # Output: Toyota Corolla

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3. Constructors

Definition:
A constructor is a special method that is automatically called when an object is created. In Python, the constructor is defined by the __init__() method.

Use-Case Example:
The constructor is used to initialize the attributes of an object when it is created.

Syntax:

class ClassName:
    def __init__(self, parameters):
        # Initialize attributes

Basic Example:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

# Creating an object
person = Person("Alice", 30)
print(person.name, person.age)  # Output: Alice 30

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4. Class, Object, and Instance Attributes

Definition:

• Class Attribute: Shared by all instances of the class.

• Object (Instance) Attribute: Unique to each object.

Use-Case Example:
Class attributes are used for constants shared by all instances, while instance attributes are specific to individual objects.

Syntax:

class ClassName:
    class_attribute = value

    def __init__(self, instance_attribute):
        self.instance_attribute = instance_attribute

Basic Example:

class Animal:
    species = "Mammal"  # Class attribute

    def __init__(self, name):
        self.name = name  # Instance attribute

dog = Animal("Dog")
cat = Animal("Cat")
print(dog.species, dog.name)  # Output: Mammal Dog
print(cat.species, cat.name)  # Output: Mammal Cat

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5. Self Parameter

Definition:
The self parameter is a reference to the current object. It is used to access attributes and methods of the class within its methods.

Use-Case Example:
self allows the methods in a class to refer to the instance calling the method.

Syntax:

class ClassName:
    def method(self):
        # Access instance variables using self

Basic Example:

class Person:
    def __init__(self, name):
        self.name = name

    def greet(self):
        return "Hello, " + self.name

# Creating an object and calling a method
person = Person("Bob")
print(person.greet())  # Output: Hello, Bob

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6. Methods in Object

Definition:
A method is a function defined inside a class that operates on the data contained in an object. Methods are used to define the behaviors of an object.

Use-Case Example:
Methods allow objects to perform actions, such as a Car class having a drive() method.

Syntax:

class ClassName:
    def method_name(self):
        # Method body

Basic Example:

class Circle:
    def __init__(self, radius):
        self.radius = radius

    def area(self):
        return 3.14 * self.radius ** 2

circle = Circle(5)
print(circle.area())  # Output: 78.5

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7. Static Method

Definition:
A static method is a method that does not access or modify the class or instance attributes. It is defined using the @staticmethod decorator.

Use-Case Example:
Static methods are used when the method logic is independent of class attributes or instance attributes.

Syntax:

class ClassName:
    @staticmethod
    def static_method():
        # Method body

Basic Example:

class Math:
    @staticmethod
    def add(a, b):
        return a + b

print(Math.add(5, 3))  # Output: 8

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8. Decorators

Definition:
Decorators are a way to modify or extend the behavior of functions or methods without modifying their code. In Python, decorators are applied using the @decorator_name syntax.

Use-Case Example:
Decorators are often used to add functionality like logging, access control, or caching to existing functions.

Syntax:

@decorator_name
def function_name():
    # Function body

Basic Example:

def decorator(func):
    def wrapper():
        print("Before function execution")
        func()
        print("After function execution")
    return wrapper

@decorator
def say_hello():
    print("Hello!")

say_hello()
# Output:
# Before function execution
# Hello!
# After function execution

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Python Basics by - Vishal Rajput