title: How do I remove duplicates from a list, while preserving order?
body: <p>How do I remove duplicates from a list, while preserving order? Using a set to remove duplicates destroys the original order.
  Is there a built-in or a Pythonic idiom?</p>
  <p>Related question: <a href="https://stackoverflow.com/questions/89178/in-python-what-is-the-fastest-algorithm-for-removing-duplicates-from-a-list-so-t">In Python, what is the fastest algorithm for removing duplicates from a list so that all elements are unique <em>while preserving order</em>?</a></p>