title: Split a list into nested lists on a value
body: <p>Say I have a list like so:</p>
  
  <pre><code>[1, 4, None, 6, 9, None, 3, 9, 4]
  </code></pre>
  
  <p>I decide to split this into nested lists on <code>None</code>, to get this:</p>
  
  <pre><code>[[1, 4], [6, 9], [3, 9, 4]]
  </code></pre>
  
  <p>Of course, I could have wanted to do this on <code>(9, None)</code> in which case, we would have got:</p>
  
  <pre><code>[[1, 4], [6], [3], [4]]
  </code></pre>
  
  <p>This is trivial to do using list append through iteration (in a for loop)</p>
  
  <p>I am interested to know whether this can be done in something faster - like a list comprehension?</p>
  
  <p>If not, why not? (for example, a list comprehension cannot return more than one list element per iteration?)</p>