Extract all the elements we're interested in.

    Returns a list of tuples with the attribute as first item
    and the list of elements as the second item.

def get_elements(html_file, tags):
    """
    Extract all the elements we're interested in.

    Returns a list of tuples with the attribute as first item
    and the list of elements as the second item.
    """
    with open(html_file) as f:
        document = BeautifulSoup(f, 'html.parser')

        def condition(tag, attr):
            # Don't include external links
            return lambda x: x.name == tag \
                and not x.get(attr, 'http').startswith(('http', '//'))

        all_tags = [(attr, document.find_all(condition(tag, attr)))
                    for tag, attr in tags]

        return all_tags