title: How to insert a character after every 2 characters in a string
body: <p>Is there a pythonic way to insert an element into every 2nd element in a string?</p>
  
  <p>I have a string: 'aabbccdd' and I want the end result to be 'aa-bb-cc-dd'.</p>
  
  <p>I am not sure how I would go about doing that.</p>