code: def get_allowed_domain(url, allow_subdomains=True):
          
          if allow_subdomains:
              return re.sub(re_www, '', re.search(r'[^/]+\.[^/]+', url).group(0))
          else:
              return re.search(re_domain, UrlExtractor.get_allowed_domain(url)).group(0)
docs: Determines the url's domain.
  
          :param str url: the url to extract the allowed domain from
          :param bool allow_subdomains: determines wether to include subdomains
          :return str: subdomains.domain.topleveldomain or domain.topleveldomain