title: Regex with strings: pairs of letters that occur twice
body: <p>How would you find pairs of letters that occur twice in a string using regex with Python?</p>
  
  <p>I want to iterate through a list of strings, find the ones that have repeating pairs of letters, and put them into a list. The letters don't need to be the same, the pair just has to repeat, though the letters can be the same.</p>
  
  <p>Ex:
  <code>xxhgfhdeifhjfrikfoixx</code> - this one has <code>xx</code> twice so I want to keep this string
  <code>kwofhdbugktrkdidhdnbk</code> - this one would be kept as well, because <code>hd</code> is repeated</p>
  
  <p>The best I got was to find the pairs: <code>([a-z][a-z])\1|([a-z])\2</code></p>
  
  <p>I need to find which strings have pairs that repeat.</p>