Django snippets

# -*- coding: utf-8 -*-
#
# Copyright (c) 2009 Arthur Furlan <arthur.furlan@gmail.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# On Debian systems, you can find the full text of the license in
# /usr/share/common-licenses/GPL-2
#
#
# Based on the django's default templatetags ifequal and ifnotequal.

from django.template import Node, NodeList, Template, Context, Variable
from django.template import TemplateSyntaxError, VariableDoesNotExist
from django.template import Library
import re

register = Library()

class IfRegexNode(Node):
        def __init__(self, var1, var2, nodelist_true, nodelist_false, negate):
                self.var1, self.var2 = Variable(var1), Variable(var2)
                self.nodelist_true, self.nodelist_false = nodelist_true, nodelist_false
                self.negate = negate

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

        def render(self, context):
                try:
                        val1 = self.var1.resolve(context)
                except VariableDoesNotExist:
                        val1 = None
                try:
                        val2 = self.var2.resolve(context)
                except VariableDoesNotExist:
                        val2 = None
                if (self.negate and not re.match(val1, val2)) or (not self.negate and re.match(val1, val2)):
                        return self.nodelist_true.render(context)
                return self.nodelist_false.render(context)

def do_ifregex(parser, token, negate):
        bits = list(token.split_contents())
        if len(bits) != 3:
                raise TemplateSyntaxError, "%r takes two arguments" % bits[0]
        end_tag = 'end' + bits[0]
        nodelist_true = parser.parse(('else', end_tag))
        token = parser.next_token()
        if token.contents == 'else':
                nodelist_false = parser.parse((end_tag,))
                parser.delete_first_token()
        else:
                nodelist_false = NodeList()
        return IfRegexNode(bits[1], bits[2], nodelist_true, nodelist_false, negate)

@register.tag
def ifregex(parser, token):
        """
        Outputs the contents of the block if the second argument matches the regular
        expression represented by the first argument.

        Examples::

                {% ifregex "^/comments/" request.path %}
                        ...
                {% endifregex %}

                {% ifnotregex "^/comments/" request.path %}
                        ...
                {% else %}
                        ...
                {% endifnotregex %}
        """
        return do_ifregex(parser, token, False)

@register.tag
def ifnotregex(parser, token):
        """
        Outputs the contents of the block if the second argument doesn't match the
        regular expression represented by the first argument.
        """
        return do_ifregex(parser, token, True)