Python Objects and Classes

1. What is a Class and an Object

A class is a blueprint for creating objects. An object is an instance of a class.

class Person:
    pass

p1 = Person()
print(p1)

Classes define structure; objects represent real entities.

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2. Defining a Class with Attributes

class Person:
    name = "Alice"
    age = 25

p = Person()
print(p.name)
print(p.age)

Attributes represent properties of the class.

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3. Constructor Method (__init__)

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

p = Person("Bob", 30)
print(p.name, p.age)

The constructor initializes object data at creation.

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4. Instance Methods

class Person:
    def __init__(self, name):
        self.name = name

    def greet(self):
        return f"Hello, my name is {self.name}"

p = Person("Alice")
print(p.greet())

Instance methods operate on object data using self.

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5. Class Variables vs Instance Variables

class Student:
    school = "Global Academy"  # Class variable

    def __init__(self, name):
        self.name = name        # Instance variable

s1 = Student("Alice")
s2 = Student("Bob")

print(s1.school)
print(s2.school)

• Class variables are shared

• Instance variables are unique per object

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6. Creating Multiple Objects

class Car:
    def __init__(self, brand):
        self.brand = brand

c1 = Car("Toyota")
c2 = Car("Tesla")

print(c1.brand)
print(c2.brand)

Multiple objects can be created from the same class.

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7. Modifying Object Properties

class Employee:
    def __init__(self, name):
        self.name = name

emp = Employee("John")
emp.name = "Michael"

print(emp.name)

Objects allow runtime modification of attributes.

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8. Deleting Object Properties and Objects

class Product:
    def __init__(self, price):
        self.price = price

item = Product(100)

del item.price
# del item  # Deletes the object entirely

Use del to remove attributes or the object itself.

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9. Built-in Object Functions

class User:
    pass

user = User()

print(isinstance(user, User))  # True
print(type(user))              # <class '__main__.User'>

Common object-related built-ins:

• type()

• isinstance()

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10. Real-World Class Example

class BankAccount:
    def __init__(self, owner, balance):
        self.owner = owner
        self.balance = balance

    def deposit(self, amount):
        self.balance += amount

    def withdraw(self, amount):
        self.balance -= amount

account = BankAccount("Alice", 1000)
account.deposit(500)
print(account.balance)  # Output: 1500

Encapsulation of data and behavior into a single unit.

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