title: Python's way to store a default value if expression failed
body: <p>What is the python analog of perl's <code>//</code> operator?</p>
  
  <p>In perl, one can do something like :</p>
  
  <pre><code>$pos = $some_list[0] // 1
  </code></pre>
  
  <p>How do you accomplish the same in python?</p>