title: How to return a website and automatically redirect to another side which takes long to load
body: <p>I ask the user to input some data, after that I redirect him to a 'result' website which takes several seconds to load. </p>
  
  <p>I don't like this, because there is no user feedback telling him, that the server has not crashed and that his result is coming. So I was thinking about showing the user a 'loading' website stating 'please wait' and then automatically redirect him to the 'result' page. The user would see the "please-wait"-website the whole time the other one is loading, as Flask does not serve the site before it is finished with the calculations.</p>
  
  <p><strong>[Attempt to clarify]</strong>
  One of the pages takes so long, because it waits for a <a href="http://flask.pocoo.org/docs/patterns/fileuploads/" rel="nofollow">file upload</a>. The other side takes  so long because its functions wait for data from a third party api.</p>
  
  <p>How would I do that in Flask? </p>