Defining Classes

A class is like a blueprint or recipe. Imagine you’re designing a blueprint for a house. The blueprint describes what the house should look like, but the actual house doesn’t exist yet. In Python:

• A class is the blueprint.
• An object is the actual house built from the blueprint.

How do you define a class?

You create a class in Python using the class keyword. Here's a basic example:

class House:
    pass

This creates a blueprint for a "House," but it doesn’t do anything yet. The pass keyword is just a placeholder when you’re not adding anything right away.

The __init__ method (Constructor)

The __init__ method is a special method (sometimes called the constructor) that runs automatically when you create an object from a class. It’s like setting up the initial state of an object. For example:

• When you build a house, you need to decide its color, number of rooms, etc.
• The __init__ method lets you set these details when creating an object.

Example: a simple class

Let’s create a House class where each house has a color and a number of rooms:

class House:
    def __init__(self, color, rooms):  # The constructor
        self.color = color            # Attribute for color
        self.rooms = rooms            # Attribute for number of rooms

Here’s what happens:

• def __init__(self, color, rooms) is the constructor. It takes two pieces of information: the house’s color and number of rooms.
• self.color = color and self.rooms = rooms store this information in the object.

Creating an object (an instance of a class)

Now let’s use the House blueprint to create an actual house:

# Creating a house object
my_house = House("blue", 3)

# Accessing attributes
print(my_house.color)  # Output: blue
print(my_house.rooms)  # Output: 3

Explanation:

• my_house = House("blue", 3) creates a house object with a blue color and 3 rooms.
• You can access the color and rooms attributes using the dot (.) notation.

Why use the __init__ method?

Without the __init__ method, you’d need to manually set all the attributes:

my_house = House()
my_house.color = "blue"
my_house.rooms = 3

The __init__ method simplifies this process by setting everything in one step.

Complete example

Here’s a fun and complete example to practice:

class Dog:
    def __init__(self, name, breed):  # Constructor
        self.name = name             # Store dog's name
        self.breed = breed           # Store dog's breed

    def bark(self):                  # A method to make the dog bark
        return f"{self.name} says Woof!"

# Creating a dog object
my_dog = Dog("Buddy", "Golden Retriever")

# Accessing attributes and methods
print(my_dog.name)       # Output: Buddy
print(my_dog.breed)      # Output: Golden Retriever
print(my_dog.bark())     # Output: Buddy says Woof!