Django templatetag for getting gravatars

gravatar.py

from django import template
from django.conf import settings
import urllib, hashlib

register = template.Library()

class GravatarUrlNode(template.Node):
    def __init__(self, email):
        self.email = template.Variable(email)

    def render(self, context):
        try:
            email = self.email.resolve(context)
        except template.VariableDoesNotExist:
            return ''

        default = settings.MEDIA_URL + 'images/defaultavatar.gif'
        size = 48

        gravatar_url = "http://www.gravatar.com/avatar/" + hashlib.md5(email).hexdigest() + "?"
        gravatar_url += urllib.urlencode({'default':default, 'size':str(size)})

        return gravatar_url

@register.tag
def gravatar_url(parser, token):
    try:
        tag_name, email = token.split_contents()

    except ValueError:
        raise template.TemplateSyntaxError, "%r tag requires a single argument" % token.contents.split()[0]

    return GravatarUrlNode(email)