post_tag.py

@register.tag
def populate_posts(parser, token):
    try:
        tag_name, num_posts, as_name, name = token.split_contents()
    except ValueError:
        raise template.TemplateSyntaxError("not enough arguments given")
    return PostsNode(num_posts, name)

class PostsNode(template.Node):
    def __init__(self, num_posts, name):
        self.num_posts = num_posts
        self.name = name

    def render(self, context):
        ""
        context[self.name] = Post.objects.filter(post_type="post",
            post_status="publish").order_by("-post_date")[:self.num_posts]
        return ""