@register.filter(is_safe=True, needs_autoescape=True)
def unordered_list(value, autoescape=None):
    """
    Recursively takes a self-nested list and returns an HTML unordered list --
    WITHOUT opening and closing <ul> tags.

    The list is assumed to be in the proper format. For example, if ``var``
    contains: ``['States', ['Kansas', ['Lawrence', 'Topeka'], 'Illinois']]``,
    then ``{{ var|unordered_list }}`` would return::

        <li>States
        <ul>
                <li>Kansas
                <ul>
                        <li>Lawrence</li>
                        <li>Topeka</li>
                </ul>
                </li>
                <li>Illinois</li>
        </ul>
        </li>
    """
    if autoescape:
        escaper = conditional_escape
    else:
        escaper = lambda x: x
    def convert_old_style_list(list_):
        """
        Converts old style lists to the new easier to understand format.

        The old list format looked like:
            ['Item 1', [['Item 1.1', []], ['Item 1.2', []]]

        And it is converted to:
            ['Item 1', ['Item 1.1', 'Item 1.2]]
        """
        if not isinstance(list_, (tuple, list)) or len(list_) != 2:
            return list_, False
        first_item, second_item = list_
        if second_item == []:
            return [first_item], True
        try:
            # see if second item is iterable
            iter(second_item)
        except TypeError:
            return list_, False
        old_style_list = True
        new_second_item = []
        for sublist in second_item:
            item, old_style_list = convert_old_style_list(sublist)
            if not old_style_list:
                break
            new_second_item.extend(item)
        if old_style_list:
            second_item = new_second_item
        return [first_item, second_item], old_style_list
    def _helper(list_, tabs=1):
        indent = u'\t' * tabs
        output = []

        list_length = len(list_)
        i = 0
        while i < list_length:
            title = list_[i]
            sublist = ''
            sublist_item = None
            if isinstance(title, (list, tuple)):
                sublist_item = title
                title = ''
            elif i < list_length - 1:
                next_item = list_[i+1]
                if next_item and isinstance(next_item, (list, tuple)):
                    # The next item is a sub-list.
                    sublist_item = next_item
                    # We've processed the next item now too.
                    i += 1
            if sublist_item:
                sublist = _helper(sublist_item, tabs+1)
                sublist = '\n%s<ul>\n%s\n%s</ul>\n%s' % (indent, sublist,
                                                         indent, indent)
            output.append('%s<li>%s%s</li>' % (indent,
                    escaper(force_unicode(title)), sublist))
            i += 1
        return '\n'.join(output)
    value, converted = convert_old_style_list(value)
    return mark_safe(_helper(value))

###################
# INTEGERS        #
###################
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/django/template/defaultfilters.py/unordered_list/original