title: Insert an element between two adjacent list elements which meet a condition
body: <p>In python, what's a clean way to insert an element between any two elements that meet a condition?</p>
  
  <p>A call like:</p>
  
  <pre><code>insert_between([1,2,3,4,7,8,9,15,16], 0, lambda x,y: x + 1 != y)
  </code></pre>
  
  <p>should produce:</p>
  
  <pre><code>[1,2,3,4,0,7,8,9,0,15,16]
  </code></pre>
  
  <p>Is there a better way than to iterate and append to second list?</p>