title: python decompose a list
body: <p>I remember I once seen a operator which is able to decompose a list in python.</p>
  
  <p>for example </p>
  
  <pre><code>[[1],[2],[3]]
  </code></pre>
  
  <p>by applying that operator, you get</p>
  
  <pre><code>[1], [2], [3]
  </code></pre>
  
  <p>what is that operator, any help will be appreciated. </p>