code: def create_app(config_filename, instance_path=None):
      
      app_ = CustomFlask(
          __name__,
          instance_path=instance_path or os.environ.get(
              'VERIPRESS_INSTANCE_PATH') or os.getcwd(),
          instance_relative_config=True
      )
      app_.config.update(dict(STORAGE_TYPE='file',
                              THEME='default',
                              CACHE_TYPE='simple',
                              MODE='view-only',
                              ENTRIES_PER_PAGE=5,
                              FEED_COUNT=10,
                              SHOW_TOC=True,
                              TOC_DEPTH=3,
                              TOC_LOWEST_LEVEL=3,
                              ALLOW_SEARCH_PAGES=True,
                              PAGE_SOURCE_ACCESSIBLE=False))
      app_.config.from_pyfile(config_filename, silent=True)
  
      theme_folder = os.path.join(app_.instance_path,
                                  'themes', app_.config['THEME'])
      # use templates in the selected theme's folder
      app_.template_folder = os.path.join(theme_folder, 'templates')
      # use static files in the selected theme's folder
      app_.theme_static_folder = os.path.join(theme_folder, 'static')
      # global static folder
      app_.static_folder = os.path.join(app_.instance_path, 'static')
  
      return app_
docs: Factory function to create Flask application object.
  
      :param config_filename: absolute or relative filename of the config file
      :param instance_path: instance path to initialize or run a VeriPress app
      :return: a Flask app object