nav bar activate in jinja

{ % set navigation_bar = [
    ('/', 'index', 'Index'),
    ('/downloads/', 'downloads', 'Downloads'),
    ('/about/', 'about', 'About')
] -%}

{ % set active_page = active_page|default('index') -%}
...
<ul id="navigation">
    { % for href, id, caption in navigation_bar %}
    <li{ % if id == active_page %} class="active"{ % endif
    %}><a href="{{ href|e }}">{{ caption|e }}</a>
    </li>
{ % endfor %}
</ul>{ % extends "layout.html" %}
{ % set active_page = "index" %}