def new_links(all_links, existing_links):
    """
    Return all links which are in the all_links but not in the existing_links.
    This is used to determine which links are new and not indexed jet. Set the
    ONLY_NEW environment variable to activate this filter mechanism.
    """
    existing_urls = {link['url'] for link in existing_links}
    return [link for link in all_links if link['url'] not in existing_urls]