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Django Template - Increment the value of a variable
{% set counter = 0 %}
{% for object in object_list %}
    {% if object.attr1 == list1.attr1 and object.attr2 = list2.attr2 %}
        <li><a href="{{ object.get_absolute_url }}"> Link {{counter++}} </a></li>
     {% endif %}
{% endfor %}

new_lst = filter(lambda x: x.attr0 == attr0 and x.attr1 == attr1, lst)

{% for object in new_lst %}
   <li><a href="{{ object.get_absolute_url }}"> Link {{ forloop.counter }} </a></li>
{% endfor %}

class IncrementVarNode(template.Node):

    def __init__(self, var_name):
        self.var_name = var_name

    def render(self,context):
        value = context[self.var_name]
        context[self.var_name] = value + 1
        return u""

def increment_var(parser, token):

    parts = token.split_contents()
    if len(parts) < 2:
        raise template.TemplateSyntaxError("'increment' tag must be of the form:  {% increment <var_name> %}")
    return IncrementVarNode(parts[1])

register.tag('increment', increment_var)

class Counter:
    count = 0

    def increment(self):
        self.count += 1

    def decrement(self):
        self.count -= 1

    def double(self):
        self.count *= 2