title: Python shorthand for array limits
body: <p>Given a <code>numpy</code> array:</p>
  
  <pre><code>a = arange(10,20,1)
  </code></pre>
  
  <p>I often need a tuple containing the first and last elements of the array:</p>
  
  <pre><code>w = a[0],a[-1]
  </code></pre>
  
  <p>Is there a handy python slicing shortcut to do this in a single reference to <code>a</code>?</p>