OOP — Classes & Objects

What a class is

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

Creating a simple class

python
class Dog:
    def __init__(self, name):
        self.name = name

fido = Dog("Fido")
print(fido.name)

The init method

__init__ runs when a new object is created. Use it to set up the initial state.

Instance attributes

Attributes are variables that belong to the object.

python
class User:
    def __init__(self, username, age):
        self.username = username
        self.age = age

Creating multiple objects

Each object has its own data.

python
u1 = User("ali", 20)
u2 = User("mona", 25)
print(u1.username)
print(u2.username)

Common mistakes to avoid

• Forgetting self in methods.
• Using a class when a simple dict would do.
• Confusing a class (blueprint) with an object (instance).

What you should understand after this lesson

• How to define a class and create objects.
• What __init__ does.
• How instance attributes store data.