How can you make a vote-up-down button like in Stackoverflow?

Problems

1. how to make an Ajax buttons (upward and downward arrows) such that the number can increase or decrease
   


2. how to save the action af an user to an variable NumberOfVotesOfQuestionID
   

I am not sure whether I should use database or not for the variable. However, I know that there is an easier way too to save the number of votes.

How can you solve those problems?

[edit]

The server-side programming language is Python.

Source: Tips4all