gistfile1.py

class VoteHandler(webapp.RequestHandler):
            
    def get(self):
        #See if logged in
        self.Session = Session()
        if not 'userkey' in self.Session:
            doRender(
                self,
                'base/index.html',
                {'error' : 'Please login to vote'})
            return
              
        #If user hasn't voted - if user doesn't have a vote on that image object
        key = self.request.get('photo_id')
        vurl = models.Image.get_by_id(int(key))
        
        #pull current site vote total & add 1
        #check user here
        vurl.votes += 1
        vurl.put()
                
        logging.info('Adding a vote')
                
        #Create a new Vote object
        newvote = models.Vote(user=self.Session['userkey'], url=vurl)
        
        newvote.put()
                
        self.redirect('/', { })

Three improvements to consider:

• Check for existing votes before adding a vote and updating the counter.
• Using a transaction to update the vote count and add the Vote object keeps the datastore in sync.. in case there are errors.
• If you need to process more than one vote (on a url) per second then sharding the counter will be required for scalability.