app engine url mapping:

• app.yaml

• -   url: /(.*)
      script: main.py
  
  url: /sites/(.*)
  script: site.py
  

-   url: /sites/(.*)
    script: site.py

url: /(.*)
script: main.py

• site.py

• class MainPage(webapp.RequestHandler):
      def get(self, site_alias):
          #do something nasty
  def main():
  application = webapp.WSGIApplication(
  [(r'/sites/(.*)', MainPage)], debug=True)
  wsgiref.handlers.CGIHandler().run(application)