Class & Object¶

Concept¶

Class	Object
A blueprint or template for creating objects	An instance of a class
Defines attributes (data) and behaviours (method) that the created objects will have	Contains data and methods defined by the class or has its own set of attribute values
Uses the `class` keyword	Created using the class name followed by parentheses
Contains the `__init__` method for initialization	Created by calling the class like a function

Implementation¶

Let's explore how to create classes and objects in Python.

Step 1: Create a Class¶

To create a class in Python, use the class keyword followed by the class name. By convention, class names are written in CamelCase.

Car is your blueprint for creating car objects. It defines the attributes and methods that each car object will have.

classDiagram
    class Car {
        +int wheels = 4
        +str brand
        +str model
        +int year
        +bool is_running
        +start()
        +stop()
    }

car.py

class Car:
  # Class attributes (shared by all instances)
  wheels = 4

  def __init__(self, brand, model, year):
    self.brand = brand # Instance attribute
    self.model = model # Instance attribute
    self.year = year # Instance attribute
    self.is_running = False # Instance attribute

  def start(self): # Instance method
    self.is_running = True
    print(f"{self.brand} {self.model} is now running.")

  def stop(self): # Instance method
    self.is_running = False
    print(f"{self.brand} {self.model} has stopped.")

- __init__() method: This is the constructor that initializes the instance attributes when a new object is created. It takes self (the instance itself) and other parameters to set the initial state of the object. - Attributes created in __init__() are called instance attributes and are unique to each object.

Step 2: Create an Object¶

classDiagram
    class Car {
        +int wheels = 4
        +str brand
        +str model
        +int year
        +bool is_running
        +start()
        +stop()
    }

    Car <|-- my_car : instance
    Car <|-- another_car : instance

car.py

class Car:
  # Class attributes (shared by all instances)
  wheels = 4

  def __init__(self, brand, model, year):
    self.brand = brand # Instance attribute
    self.model = model # Instance attribute
    self.year = year # Instance attribute
    self.is_running = False # Instance attribute

  def start(self): # Instance method
    self.is_running = True
    print(f"{self.brand} {self.model} is now running.")

  def stop(self): # Instance method
    self.is_running = False
    print(f"{self.brand} {self.model} has stopped.")

# Creating objects (instances)
my_car = Car("BMW", "X5", 2020)
another_car = Car("Audi", "A4", 2021)

# Accessing attributes and methods
print(my_car.brand) # BMW
my_car.start() # BMW X5 is now running!
print(my_car.is_running) # True