title: Discontinuous slice in python list
body: <p>I'm looking for an efficient way of achieving this, which I think is a slicing-like operation:</p>
  
  <pre><code>&gt;&gt;&gt; mylist = range(100)
  &gt;&gt;&gt;magicslicer(mylist, 10, 20)
  [0,1,2,3,4,5,6,7,8,9,30,31,32,33,34,35,36,37,38,39,60,61,62,63......,97,98,99]
  </code></pre>
  
  <p>the idea is: the slicing gets 10 elements, then <em>skips</em> 20 elements, then gets next 10, then skips next 20, and so on.</p>
  
  <p>I think I should not use loops if possible, for the very reason to use slice is (I guess) to do the "extraction" efficiently in a single operation.</p>
  
  <p>Thanks for reading.</p>