title: Using replace() method in python by index
body: <p>I want to do something like this.</p>
  
  <pre><code>example_string = "test"
  print(example_string.replace(example_string[0], "b"))
  </code></pre>
  
  <p>expecting the output</p>
  
  <pre><code>best
  </code></pre>
  
  <p>however because the letter "t" is being passed into the method the t at the end also gets replaced with a "b". Resulting in the output</p>
  
  <pre><code>besb
  </code></pre>
  
  <p>How do I do it in a way that would result in the output "best" instead of "besb"?</p>