code: def _get_url(self, filename):
          
          return self.cdn_url.format(self.mver, self.relnum, filename)
docs: Returns url for cdn.urbanterror.info to pass to _not_wget().
  
          http://cdn.urbanterror.info/urt/<major_ver_without_.>/<release_num>-<magic_number>/q3ut4/<filename>