code: def route_to_alt_domain(request, url):
      
  
      # Do we need to route IPython Notebook request from a different location
      alternative_domain = request.registry.settings.get("pyramid_notebook.alternative_domain", "").strip()
      if alternative_domain:
          url = url.replace(request.host_url, alternative_domain)
  
      return url
docs: Route URL to a different subdomain.
  
      Used to rewrite URLs to point to websocket serving domain.