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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def subdomain(self, hostname):
 """ Determine of which known domain the given hostname is a subdomain. @return: A two-tuple giving the subdomain part and the domain part or C{None} if the domain is not a subdomain of any known domain. """

        hostname = hostname.split(":")[0]
        for domain in getDomainNames(self.siteStore):
            if hostname.endswith("." + domain):
                username = hostname[:-len(domain) - 1]
                if username != "www":
                    return username, domain
        return None