code: def update_rating(self, postid):
          '''
          only the used who logged in would voting.
          '''
          post_data = self.get_post_data()
          rating = float(post_data['rating'])
          postinfo = MPost.get_by_uid(postid)
          if postinfo and self.userinfo:
              MRating.update(postinfo.uid, self.userinfo.uid, rating=rating)
              self.update_post(postid)
          else:
              return Falsf update_rating(self, postid):
          '''
          only the used who logged in would voting.
          '''
          post_data = self.get_post_data()
          rating = float(post_data['rating'])
          postinfo = MPost.get_by_uid(postid)
          if postinfo and self.userinfo:
              MRating.update(postinfo.uid, self.userinfo.uid, rating=rating)
              self.update_post(postid)
          else:
              return False
docs: only the used who logged in would voting.