title: Replace nth occurrence of substring in string
body: <p>I want to replace the n'th occurrence of a substring in a string.</p>
  
  <p>There's got to be something equivalent to what I WANT to do which is </p>
  
  <p><code>mystring.replace("substring", 2nd)</code></p>
  
  <p>What is the simplest and most Pythonic way to achieve this?</p>
  
  <p><strong>Why not duplicate:</strong> I don't want to use regex for this approach and most of answers to similar questions I found are just regex stripping or really complex function. I really want as simple as possible and not regex solution.</p>