def fetch_element_att(html, css, attr):
    """
    Fetch the given elements specifed by the css selector from html
    (an `Element` from lxml) and return the attribute (attr) of each.
    """
    rv = None
    elements = html.cssselect(css)
    if len(elements) == 1:
        rv = elements[0].get(attr)
    elif len(elements) > 1:
        rv = ';'.join([e.get(attr) for e in elements])
    return rv