Python Day 5: Python Classes

1. Defining a Simple Class

In Python, a class is a blueprint for creating objects (a particular data structure). It defines a set of attributes and methods that characterize any object of the class.

# Defining a basic class
class Dog:
    def __init__(self, name, age):  # The __init__ method initializes object attributes
        self.name = name  # Attribute
        self.age = age    # Attribute

# Creating an object (instance) of the Dog class
dog1 = Dog("Buddy", 5)

# Accessing attributes
print(dog1.name)  # Output: Buddy
print(dog1.age)   # Output: 5

2. Adding Methods to a Class

Methods are functions defined inside a class that describe the behaviors of an object. Here’s an example where we add a bark method to the Dog class:

# Adding methods to a class
class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def bark(self):  # Method
        return "Woof!"

# Creating an object and calling its method
dog1 = Dog("Buddy", 5)
print(dog1.bark())  # Output: Woof!

3. The `init` Method (Constructor)

The __init__ method is called a constructor. It is a special method that is automatically invoked when a new object of the class is created. It’s used to initialize the object’s attributes:

# The __init__ method (constructor) initializes object attributes
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

# Creating a new Person object
person1 = Person("Alice", 30)
print(person1.name)  # Output: Alice
print(person1.age)   # Output: 30

4. Inheritance

Inheritance allows a class to inherit attributes and methods from another class. Here, we have a base class Animal and a derived class Cat that inherits from it:

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

    def speak(self):  # Base method
        return "Some sound"

class Cat(Animal):  # Cat inherits from Animal
    def speak(self):  # Overriding the base method
        return "Meow!"

# Creating an object of the Cat class
cat1 = Cat("Whiskers")
print(cat1.name)       # Output: Whiskers
print(cat1.speak())    # Output: Meow!

5. Encapsulation

Encapsulation is the practice of keeping certain data private within a class. Attributes prefixed with double underscores __ are treated as private and cannot be accessed directly from outside the class.

# Encapsulation in Python
class BankAccount:
    def __init__(self, balance=0):
        self.__balance = balance  # Private attribute

    def deposit(self, amount):  # Method to modify private attribute
        self.__balance += amount

    def get_balance(self):  # Getter method
        return self.__balance

# Creating a BankAccount object
account = BankAccount()
account.deposit(100)
print(account.get_balance())  # Output: 100

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