__init__.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from os import path

db = SQLAlchemy()
DB_NAME = 'database.db'

def create_app():
    app = Flask(__name__)
    app.config['SECRET_KEY'] = 'fdadjfaoef afdpp'
    app.config['SQLALCHEMY_DATABASE_URI'] = f'sqlite:///{DB_NAME}' #This stores sqlite database in current dir

    db.init_app(app) #This show what is app our database is storing

    from .views import views
    from .auth import auth

    app.register_blueprint(views,url_prefix='/')
    # app.register_blueprint(auth,url_prefix='/auth/') #What's different between both this here before every url it must /auth/ then what you want
    app.register_blueprint(auth,url_prefix='/')      #It will be / only no prefix-> before url
    
    from .models import User,Note
    create_database()    

    return app

def create_database():
    if not path.exists('website/'+DB_NAME):
        print("Created Database!")