title: Partial page updates
body: <p>i am currently writing a python web-application running on google-app-engine using the webapp2  framework. Since i am not the web-guy i need an advice how to solve the following problem:</p>
  
  <p>Assumed i have a very simple web order system where you put some articles in the shopping card and proceed to the checkout form... On the checkout form i need to display the total cost of the order. The problem is that there is also a combobox where the customer can choose a shipping method. Each shipping method has its individual transportation costs.</p>
  
  <p>The question is how can i calculate and update the total cost (including the selected shipping method and its transportation costs) without reloading the whole page?
  Doing the calculations with client side Javascript seems to be inappropriate solution the me. But who to do the calculation on the server-side without reloading the whole page?</p>