class ServeHandler(blobstore_handlers.BlobstoreDownloadHandler):

    def get(self, resource):
        resource = str(urllib.parse.unquote(resource))
blob_info = blobstore.BlobInfo.get(resource)
self.send_blob(blob_info)

def main():
    application = webapp.WSGIApplication([('/', MainHandler), ('/upload',
        UploadHandler), ('/serve/([^/]+)?', ServeHandler)], debug=True)
run_wsgi_app(application)
if __name__ == '__main__':
    main()
Upload a file in Google App Engine and making it downloadable