__init__ & self

init — the constructor

__init__ is Python's constructor — it runs automatically when you create an object, just like TypeScript's constructor.

TypeScript:

class User {
  name: string;
  age: number;

  constructor(name: string, age: number) {
    this.name = name;
    this.age = age;
  }
}

const user = new User('John', 25);

Python:

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

user = User("John", 25)

self — Python's this

self refers to the current object, same job as this in TypeScript. The key difference: self must be written explicitly as the first parameter of every method — Python never adds it for you invisibly like JS/TS does with this.

def __init__(self, name, age):
    self.name = name   # self.<anything> = an instance variable
    self.age = age

Instance variables

self.name and self.age are instance variables — data that belongs to that one specific object, exactly like this.name in a TS class. Each object you create gets its own copy:

john = User("John", 25)
david = User("David", 30)

print(john.name)    # John
print(david.name)   # David