Classes and Objects

Introduction

Object-Oriented Programming (OOP) organises code around objects — bundles of related data and behaviour. A class is the blueprint; an object (or instance) is what you create from it.

Defining a Class

class Employee:
    pass   # empty class for now

Creating an Instance

emp = Employee()
print(type(emp))   # <class '__main__.Employee'>

The init Method

__init__ is called automatically when a new instance is created. Use it to set the initial state of the object.

class Employee:
    def __init__(self, firstname, lastname, department, salary):
        self.firstname = firstname
        self.lastname = lastname
        self.department = department
        self.salary = salary

emp = Employee("Alice", "Smith", "Engineering", 80000)
print(emp.firstname)    # Alice
print(emp.salary)       # 80000

self refers to the instance being created. It must be the first parameter of every method, though you never pass it yourself when calling.

Accessing Attributes

emp = Employee("Alice", "Smith", "Engineering", 80000)

# Read
print(emp.department)

# Update
emp.salary = 85000
print(emp.salary)

Practice Exercises

• Define a Product class with attributes name, category, and price.
• Create three Product instances with different values and print all their attributes.
• Update the price of one product and print it again to confirm the change.
• Create a list of five Product objects and use a loop to print each product's name and price.