rules = Rule(RCP_RegexLinkExtractor(allow=
    'epolls/2012/president/[a-z]{2}/[a-z]+_romney_vs_obama-[0-9]{4}\\.html',
    allow_domains=('realclearpolitics.com',)), callback='parseStatePolls',
    process_links='processLinks', process_request='processRequest'),
How can i write my custom link extractor in scrapy python