title: Replacing one item in a list with two items
body: <p>What is the simplest method for replacing one item in a list with two?</p>
  
  <p>So:</p>
  
  <pre><code>list=['t' , 'r', 'g', 'h', 'k']
  </code></pre>
  
  <p>if I wanted to replace 'r' with 'a' and 'b':</p>
  
  <pre><code>list = ['t' , 'a' , 'b', 'g', 'h', 'k']
  </code></pre>