def _get_select_list_options_selected(self, locator):
select = self._get_select_list(locator)
# TODO: Handle possible exception thrown by all_selected_options
return select, select.all_selected_options
方法名：_get_select_list_options_selected(self, locator)
私有方法 返回Select 元素对象和选中options集合
接收参数：locator
第2行：否则使用_get_select_list(self, locator)方法，返回Select对象
第4行：返回Select 元素对象和选中options集合