@register.function
@jinja2.contextfunction
def impala_breadcrumbs(context, items=list(), add_default=True, crumb_size=40):
    """
    show a list of breadcrumbs. If url is None, it won't be a link.
    Accepts: [(url, label)]
    """
    if add_default:
        base_title = page_name(context['request'].APP)
        crumbs = [(urlresolvers.reverse('home'), base_title)]
    else:
        crumbs = []

    # add user-defined breadcrumbs
    if items:
        try:
            crumbs += items
        except __HOLE__:
            crumbs.append(items)

    crumbs = [(url, truncate(label, crumb_size)) for (url, label) in crumbs]
    c = {'breadcrumbs': crumbs, 'has_home': add_default}
    t = get_env().get_template('amo/impala/breadcrumbs.html').render(c)
    return jinja2.Markup(t)
dataset/ETHPy150Open mozilla/addons-server/src/olympia/amo/helpers.py/impala_breadcrumbs