title: List vs tuple, when to use each?
body: <p>In Python, when should you use lists and when tuples?</p>
  
  <p>Sometimes you don't have a choice, for example if you have</p>
  
  <pre><code>"hello %s you are %s years old" % x
  </code></pre>
  
  <p>then x must be a tuple.</p>
  
  <p>But if I am the one who designs the API and gets to choose the data types, then what are the guidelines?</p>