title: Python index more than once
body: <p>I know that <code>.index()</code> will return where a substring is located in python. 
  However, what I want is to find where a substring is located for the nth time, which would work like this:</p>
  
  <pre><code>&gt;&gt; s = 'abcdefacbdea'
  &gt;&gt; s.index('a')
  0
  &gt;&gt; s.nindex('a', 1)
  6
  &gt;&gt;s.nindex('a', 2)
  11
  </code></pre>
  
  <p>Is there a way to do this in python?</p>