title: Concept of python slicing method
body: <p>I have below list</p>
  
  <pre><code>l1 = [1,2,3,4,5,6,7,8,9]
  </code></pre>
  
  <p>I want to understand below 
  result :-</p>
  
  <pre><code>&gt;&gt;&gt; l1
  [4:8:-2]
  </code></pre>
  
  <p>Please explain result of above slicing.</p>