Determines the domain's subdomains.

        :param str url: the url to extract any subdomains from
        :return str: subdomains of url

def get_subdomain(url):
        """
        Determines the domain's subdomains.

        :param str url: the url to extract any subdomains from
        :return str: subdomains of url
        """
        allowed_domain = UrlExtractor.get_allowed_domain(url)
        return allowed_domain[:len(allowed_domain) - len(
            UrlExtractor.get_allowed_domain(url, False))]