docs: def get_site_url():
      """Returns a URL for current site.
  
      :rtype: str|unicode
  
      """
      site_url = getattr(_THREAD_LOCAL, _THREAD_SITE_URL, None)
      if site_url is None:
          site_url = SITE_URL or get_site_url_()
          setattr(_THREAD_LOCAL, _THREAD_SITE_URL, site_url)
  
      return site_url