docs: def get_host(self, domain_part):
          """Figures out the full host name for the given domain part.  The
          domain part is a subdomain in case host matching is disabled or
          a full host name.
          """
          if self.map.host_matching:
              if domain_part is None:
                  return self.server_name
              return to_unicode(domain_part, "ascii")
          subdomain = domain_part
          if subdomain is None:
              subdomain = self.subdomain
          else:
              subdomain = to_unicode(subdomain, "ascii")
          return (subdomain + u"." if subdomain else u"") + self.server_name