05 - Understanding Object-Oriented Programming (OOP) in Python

• python
• by Sn0wAlice

Introduction

Object-Oriented Programming (OOP) is a programming paradigm based on the concept of objects, which encapsulate data and behavior. Python supports OOP through classes and objects, enabling modular and reusable code.

---

1. Defining Classes and Creating Objects

Creating a Class

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

    def greet(self):
        return f"Hello, my name is {self.name} and I am {self.age} years old."

Creating an Object

person1 = Person("Alice", 25)
print(person1.greet())

---

2. Class Attributes and Instance Attributes

Instance Attributes (Unique to Each Object)

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

car1 = Car("Toyota", "Camry")
car2 = Car("Honda", "Civic")
print(car1.brand, car2.brand)  # Output: Toyota Honda

Class Attributes (Shared Across All Objects)

class Employee:
    company = "TechCorp"  # Class attribute

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

emp1 = Employee("John")
print(emp1.company)  # Output: TechCorp

---

3. Methods in Classes

Instance Methods (Operate on Object Instance)

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

    def bark(self):
        return f"{self.name} says Woof!"

dog1 = Dog("Buddy")
print(dog1.bark())

Class Methods (Operate on Class-Level Data)

class Animal:
    species = "Mammal"

    @classmethod
    def get_species(cls):
        return cls.species

print(Animal.get_species())  # Output: Mammal

Static Methods (Independent of Class & Instance)

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

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

---

4. Inheritance (Extending Classes)

Basic Inheritance

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

    def speak(self):
        return "I make a sound"

class Dog(Animal):
    def speak(self):
        return "Woof!"

dog = Dog("Buddy")
print(dog.speak())  # Output: Woof!

Overriding Methods

class Parent:
    def show(self):
        return "Parent Method"

class Child(Parent):
    def show(self):
        return "Child Method"

c = Child()
print(c.show())  # Output: Child Method

---

5. Encapsulation and Private Variables

Encapsulation restricts direct access to object data.

Private Attributes and Methods

class BankAccount:
    def __init__(self, balance):
        self.__balance = balance  # Private attribute

    def deposit(self, amount):
        self.__balance += amount
        return self.__balance

account = BankAccount(1000)
print(account.deposit(500))  # Output: 1500
# print(account.__balance)  # This will raise an AttributeError

---

Exercises

• Create a Student class with attributes name, grade, and a method to print student details.
• Implement a Vehicle class with a Car subclass that overrides a method.
• Create a Calculator class with a static method for multiplication.
• Implement encapsulation by defining a private attribute in a class.

---

Conclusion

You have now learned Object-Oriented Programming (OOP) in Python, covering classes, objects, inheritance, encapsulation, and polymorphism. The next step is to learn about file handling and exception handling in Python.

---