get_products template tag for django >mezzanine > cartridge (Work in progress)

get_products.py

from django import template
from django.db.models import get_model

register = template.Library()

class ProductContentNode(template.Node):
    def __init__(self, num, varname):
        model = 'shop.Product'
        self.num = int(num)
        self.num_check = num*4
        self.varname = varname
        self.model = get_model(*model.split('.'))

    def render(self, context):
        mod = self.model._default_manager.all().order_by('-id')[:self.num_check]
        special_list = []
        latest_list = []
        for prod in mod:
            if prod.on_sale():
                special_list.append(prod)
            else:
                latest_list.append(prod)
        special_list = special_list[:self.num]
        latest_list = latest_list[:self.num]
        context[self.varname] = {'specials':special_list, 'latest': latest_list}
        return ''

@register.tag()
def get_products(parser, token):
    # Syntax
    # {% get_products 4 as products %}
    bits = token.contents.split()
    if len(bits) !=4:
        raise template.TemplateSyntaxError, "get_products tag takes exactly Four arguments"
    if bits[2] != 'as':
        raise template.TemplateSyntaxError, "Third argument to get_products tag must be 'as'"
    return ProductContentNode(bits[1],bits[3])