text: import os
  from flask import Flask
  
  def create_app(test_config=None):
      # Create and configure the app
      app = Flask(__name__, instance_relative_config=True)
      app.config.from_mapping(
          SECRET_KEY = 'dev',
          DATABASE = os.path.join(app.instance_path, 'flaskr.sqlite')
      )
  
      if test_config is None:
          # load the instance config, if it exist, when not testing
          app.config.from_pyfile('config.py', silent=True)
      else:
          # load the test config if passed in
          app.config.from_mapping(test_config)
  
      # ensure the instance folder exists
      try:
          os.makedirs(app.instance_path)
      except OSError:
          pass
  
      from . import db, auth, blog
      db.init_app(app)    
  
      app.register_blueprint(auth.bp)
      app.register_blueprint(blog.bp)
      app.add_url_rule('/', endpoint='index')
  
      @app.route('/hello')
      def hello():
          return 'Hello, World!'
  
      return app