def diff(what_should_be, what_is):
    """
    Accept what_should_be (dict of name: ip)
    and what_is (dict of name: ip)
    Return dict of name: ip with ip from 'what_should_be' where 'what_is' does
    not match 'what_should_be'.
    """
    return {
        name: ip
        for name, ip in what_should_be.items()
        if what_should_be[name] != what_is.get(name, None)
    }