title: Why doesn't the python slice syntax wrap around from negative to positive indices?
body: <p>I noticed, given <code>l = [1,2,3]</code>, that <code>l[-1:]</code> returns <code>[3]</code> as expected, but that <code>l[-1:0]</code> returns <code>[]</code>, very much unlike what I expected.
  I then tried <code>[-1:1]</code>, which I expected to return <code>[3,1]</code>, but it also returns <code>[]</code>.</p>
  
  <p>Is there a good reason why the slice syntax does not wrap around from negative to positive indices (and the other way round)?</p>
  
  <p>It seems it would be pretty useful and pretty straightforward to implement, but maybe I'm missing something.</p>