Objective:
Understand classes, objects, and key OOP concepts in Python to write modular, reusable, and organized code.
Topics and Examples:
1. Classes & Objects
Classes are blueprints for creating objects; objects are instances of classes.
Example:
class Person:
pass # Empty class
# Creating an object
person1 = Person()
print(person1) # <__main__.Person object at 0x...>
2. Attributes & Methods
Attributes store data; methods define behavior for the object.
Example:
class Person:
species = "Human" # Class attribute
def greet(self, name): # Method
print(f"Hello {name}, I am a {self.species}")
person1 = Person()
person1.greet("Chinmaya") # Hello Chinmaya, I am a Human
3. __init__() Constructor
The __init__() method initializes object attributes during creation.
Example:
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def greet(self):
print(f"Hello, my name is {self.name} and I am {self.age} years old.")
person1 = Person("Chinmaya", 25)
person1.greet()
4. Encapsulation: Private/Public Attributes
Encapsulation restricts access to class attributes for data security.
- Public attributes: accessible from anywhere
- Private attributes: prefix with
__ (double underscore)
Example:
class Person:
def __init__(self, name, age):
self.name = name # Public
self.__age = age # Private
def get_age(self):
return self.__age # Access private attribute
person1 = Person("Chinmaya", 25)
print(person1.name) # Chinmaya
print(person1.get_age()) # 25
# print(person1.__age) # Error: Private attribute
5. Inheritance & Polymorphism
Inheritance allows a class to derive from another class. Polymorphism allows methods to have different behavior in child classes.
Example:
class Person:
def greet(self):
print("Hello from Person")
class Student(Person): # Inherits from Person
def greet(self): # Polymorphism / Method overriding
print("Hello from Student")
person = Person()
student = Student()
person.greet() # Hello from Person
student.greet() # Hello from Student
6. Method Overriding
A child class can override a parent class method to change its behavior. (Covered in the example above under Polymorphism)
Example:
class Person:
def greet(self):
print("Hello from Person")
class Student(Person):
def greet(self): # Overriding parent method
print("Hello from Student")
student = Student()
student.greet() # Hello from Student
7. Special Methods: __str__(), __repr__(), __len__()
Special methods (dunder methods) customize object behavior.
Example:
class Book:
def __init__(self, title, pages):
self.title = title
self.pages = pages
def __str__(self):
return f"Book: {self.title}"
def __repr__(self):
return f"Book('{self.title}', {self.pages})"
def __len__(self):
return self.pages
book = Book("Python Programming", 300)
print(book) # Book: Python Programming
print(repr(book)) # Book('Python Programming', 300)
print(len(book)) # 300
This section covers all essential OOP concepts in Python, including classes, objects, encapsulation, inheritance, polymorphism, method overriding, and special methods, with practical examples for better understanding.
