code: def init_app(self, app):
          
          # Ensure SECRET_KEY is set.
          SECRET_KEY = app.config.get('SECRET_KEY')
  
          if SECRET_KEY is None:
              app.config['SECRET_KEY'] = 'CHANGE_ME'
              warnings.warn(
                  'Set configuration variable SECRET_KEY with random string',
                  UserWarning)
docs: Initialize Flask application.