title: Pass list to function by value
body: <p>I want to pass a list into function by value.
  By default, lists and other complex objects passed to function by reference.
  Here is some desision:</p>
  
  <pre><code>def add_at_rank(ad, rank):
      result_ = copy.copy(ad)
      .. do something with result_
      return result_
  </code></pre>
  
  <p>Can this be written shorter?
  In other words, I wanna not to change <strong>ad</strong>.</p>