def build_versatileimagefield_url_set(image_instance, size_set, request=None):
size_set = validate_versatileimagefield_sizekey_list(size_set)<EOL>to_return = {}<EOL>if image_instance or image_instance.field.placeholder_image:<EOL><INDENT>for key, image_key in size_set:<EOL><INDENT>img_url = get_url_from_image_key(image_instance, image_key)<EOL>if request is not None:<EOL><INDENT>img_url = request.build_absolute_uri(img_url)<EOL><DEDENT>to_return[key] = img_url<EOL><DEDENT><DEDENT>return to_return<EOL>
Return a dictionary of urls corresponding to size_set
- `image_instance`: A VersatileImageFieldFile
- `size_set`: An iterable of 2-tuples, both strings. Example:
    [
        ('large', 'url'),
        ('medium', 'crop__400x400'),
        ('small', 'thumbnail__100x100')
    ]

    The above would lead to the following response:
    {
        'large': 'http://some.url/image.jpg',
        'medium': 'http://some.url/__sized__/image-crop-400x400.jpg',
        'small': 'http://some.url/__sized__/image-thumbnail-100x100.jpg',
    }
- `request`: