Templates Tags in Django 1.9.x as tools for list manipulations

lists.py

from django.template.library import Library

register = Library()


@register.filter
def split(s, sep= None):
    '''
        Example:
            {# For details on 'assign' tag, see https://gist.github.com/corebreaker/6d94b7d06f7ed9d8bfc4985b094bf6d4 #}
            {% assign 'A,B,C' as my_string %}

            <ul>
                {% for i in my_string|split:',' }}
                    <li>{{ i }}</li>
                {% endfor %}
            </ul>

        Result:
            <ul>
                <li>A</li>
                <li>B</li>
                <li>C</li>
            </ul>
    '''
    return (s or '').split(sep or ' ')


@register.filter
def inlist(l, value):
    return (value or '') in (l or [])


@register.filter
def list_filter(lst, attr_name):
    attr_name = attr_name or ''

    def get_attr(val):
        if hasattr(val, '__getitem__') and callable(val.__getitem__):
            try:
                return val[attr_name]
            except:
                pass

        return getattr(val, attr_name, False)

    return [elt for elt in (lst or []) if get_attr(elt)]


@register.filter
def find_first(lst, attr_name):
    attr_name = attr_name or ''
    
    def get_attr(val):
        if hasattr(val, '__getitem__') and callable(val.__getitem__):
            try:
                return val[attr_name]
            except:
                pass

        return getattr(val, attr_name, False)

    res, idx = -1, 0
    for elt in (lst or []):
        if get_attr(elt):
            res = idx
            break

        idx += 1

    return res


@register.simple_tag(name= 'make-list')
def make_list(*values):
    return list(values)


@register.simple_tag(name= 'list-values')
def list_values(*values):
    '''
        Examples:
            {% values 'A' 'B' 'C' as a_var %}
            {% values 1 'A' this as my_list %}

        'values' statement makes better and easier that old way to make lists:
            {{ 'ABC'|make_list }}
    '''
    return values


@register.simple_tag(name= 'make-range')
def make_range(start_stop, stop= None, step= None):
    '''
        Examples:
            {% range 10 as list1 %}
            {% for i in list1 %}
                {{ i }}
            {% endfor %}

            {% range 0 10 2 as list2 %}
            {% for i in list2 %}
                {{ i }}
            {% endfor %}
    '''
    try:
        step = int(step or 1)
    except ValueError:
        step = 1
    
    start_stop = int(start_stop or 0)
    if stop is None:
        if abs(step) > 1:
            range(0, start_stop, step)

        return range(start_stop)
    else:
        stop = int(stop or 0)

    return range(start_stop, stop, step)


@register.simple_tag(name= 'concat-list')
def concat_lists(*lists):
    '''
        Common operator for lists, concatenate lists passed as parameters:
        {% concatlists list1 list2 list3 as new_list %}
    '''
    res = []
    for l in lists:
        res += list(l or [])

    return res


@register.filter('embed-list')
def embed_list(val, prefix_suffix):
    '''
        {# For details on 'assign' tag, see https://gist.github.com/corebreaker/6d94b7d06f7ed9d8bfc4985b094bf6d4 #}
        {% assign 'A,B,C' as my_old_string %}

        {{ my_old_string |split:',' |embedlist:'[,]' |join ', ' }}
        Equals to:
        [{{ my_old_string |split:',' |join:'], [' }}]
    '''
    prefix, suffix = str(prefix_suffix).split(',', 1)

    return [(prefix + v + suffix) for v in val]


@register.simple_tag(name= 'make-set')
def make_set(*values):
    return set(values)


@register.simple_tag(name= 'make-set')
def set_add(set_value, *values):
    set_value.add(*values)

    return ''