Random image rotators everywhere

After I came across this I decided that I should write something about the same thing but done in Nevow.
First of all the task is to write a random image rotation implementation for jpegs, gifs and pngs. This is easily accomplished by doing the following 3 things:

1. Add this to the root Page of your web site. 'random/images/directory' is a directory in your HDD containing lots of images and other random data.

child_random_images = static.File('random/images/directory')

2. Add this to each of your Page objects that use the random image (or use a common base class to have this behaviour everywhere for free):

 
def render_random_image(self, ctx, data):
    files = [f for f in os.listdir('random/images/directory') 
               if os.path.splitext(f)[1] in ['.jpg', '.gif', '.png']]
    return ctx.tag(src='/random_images/'+random.choice(files))
    

3. Use the following tag wherever you want to have a randomly rotated image in your web app:

 <img nevow:render="random_image" alt="Random Image" /> 

Now you have a wonderfully randomly rotated image in your web browser and with 2 lines less than the Ruby On Rails counterpart without sacrifying readability too much.