code: def create_app(test_config=None):
      """Create and configure an instance of the Flask application."""
      app = Flask(__name__, instance_relative_config=True)
      app.config.from_mapping(
          # a default secret that should be overridden by instance config
          SECRET_KEY="dev",
          # store the database in the instance folder
          DATABASE=os.path.join(app.instance_path, "flaskr.sqlite"),
      )
  
      if test_config is None:
          # load the instance config, if it exists, when not testing
          app.config.from_pyfile("config.py", silent=True)
      else:
          # load the test config if passed in
          app.config.update(test_config)
  
      # ensure the instance folder exists
      try:
          os.makedirs(app.instance_path)
      except OSError:
          pass
  
      @app.route("/hello")
      def hello():
          return "Hello, World!"
  
      # register the database commands
      from . import db
  
      db.init_app(app)
  
      # apply the blueprints to the app
      from . import auth
      from . import blog
  
      app.register_blueprint(auth.bp)
      app.register_blueprint(blog.bp)
  
      # make url_for('index') == url_for('blog.index')
      # in another app, you might define a separate main index here with
      # app.route, while giving the blog blueprint a url_prefix, but for
      # the tutorial the blog will be the main index
      app.add_url_rule("/", endpoint="index")
  
      return app
  
label_desc: Use image node_id 1 for calling a global function with example usage: create_app(test_config) and returns: app, str