Classes

Classes are blueprints for objects. __init__() is the constructor; self refers to the instance.

Inheritance

Child classes reuse parent behavior. Use super().__init__() for parent constructor.

Polymorphism

Different classes share the same interface. Python uses duck typing.

Syntax

PYTHON

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class Dog:
    def __init__(self, name, breed):
        self.name = name
        self.breed = breed
    def bark(self): return f"{self.name} says Woof!"

class Animal:
    def speak(self): raise NotImplementedError

class Cat(Animal):
    def speak(self): return f"{self.name} says Meow!"

ES6 Classes

JAVASCRIPT

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class Animal {
    constructor(name, sound) {
        this.name = name;
        this.sound = sound;
    }

    speak() {
        return this.name + " says " + this.sound;
    }
}

class Dog extends Animal {
    constructor(name) {
        super(name, "Woof");
    }

    fetch() {
        return this.name + " is fetching!";
    }
}

let dog = new Dog("Buddy");
console.log(dog.speak());
console.log(dog.fetch());

Try It Yourself

Practice

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Exercise

Create a Student class with name, grades, and GPA method.

Answer

class Student:
    def __init__(self, name):
        self.name = name
        self.grades = []
    def add_grade(self, g): self.grades.append(g)
    def gpa(self): return sum(self.grades)/len(self.grades) if self.grades else 0

Quick Quiz

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What does self represent?

The class

The current instance

The parent

self refers to the current instance.

Retry Quiz

Interview Questions

Class vs instance variables?

Instance vars (self.x) are per-object. Class vars are shared across all instances.

Tutorial Complete

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