{% with %} template tag

# NOTE: This tag is now in Django core, so if you have Django >0.96 (or SVN)
# then you do NOT need this.

from django.template import Library
from django.template import Node, NodeList
from django.template import TemplateSyntaxError

register = Library()

#@register.tag
def do_with(parser, token):
    """
    Add a value to the context (inside of this block) for easy access.

    Example::

        {% with person.addresses.all as addresses %}
            {% if addresses %}
                <h3>Addresses</h3>
                {% for address in addresses %}
                   ...
                {% endfor %}
            {% endif %}
        {% endwith %}
    """
    bits = list(token.split_contents())
    if len(bits) != 4 or bits[2] != "as":
        raise TemplateSyntaxError, "%r expected format is 'value as name'" % tagname
    var = parser.compile_filter(bits[1])
    name = bits[3]
    nodelist = parser.parse(('endwith',))
    parser.delete_first_token()
    return WithNode(var, name, nodelist)
do_with = register.tag('with', do_with)

class WithNode(Node):
    def __init__(self, var, name, nodelist):
        self.var = var
        self.name = name
        self.nodelist = nodelist

    def __repr__(self):
        return "<WithNode>"

    def render(self, context):
        val = self.var.resolve(context)
        context.push()
        context[self.name] = val
        output = self.nodelist.render(context)
        context.pop()
        return output