title: Inserting "-" in string after elements of variable lengths
body: <p>Is there a way to convert the string                 <strong>"12345678aaaa12345678bbbbbbbb"</strong> to <strong>"12345678-aaaa-1234-5678-bbbbbbbb"</strong> in python?</p>
  
  <p>I am not sure on how to do it, since I need to insert "-" after elements of variable lengths say after 8th element then 4th element and so on.</p>