title: How do I enforce unique user names in Flask?
body: <p>I'm a complete beginner to Flask and I'm starting to play around with making web apps. </p>
  
  <p>I have a hard figuring out how to enforce unique user names. I'm thinking about how to do this in SQL, maybe with something like <code>user_name text unique on conflict fail</code>, but then how to I catch the error back in Python?</p>
  
  <p>Alternatively, is there a way to manage this that's built in to Flask?</p>