HTML editor for Google App Engine
application = webapp.WSGIApplication([  ('/page/([0-9]+)', PageHandler), ])


I'd put the list of urls as a global constant, I think that would make it easier to read.

  class PageHandler(BaseHandler):
      def get(self, file_id):
        page = Page.get_by_id(long(file_id))
        if not page:


If you are checking against None here, I'd  use if page is None:

  self.error(404)
  return


I'd use else instead of returning here

self.render_template(file_id+'.html', {
    'body': page.body,
})