title: Python split iterables into combinations
body: <p>given a iterable <code>'ABCD'</code>, I'd like to get all <code>(1,3)</code> pairs, eg:</p>
  
  <pre><code>('A', 'BCD'),
  ('B', 'ACD'),
  ('C', 'ABD'),
  ('D', 'ABC')
  </code></pre>
  
  <p>I've found <code>itertools.combination</code>, however, it can only give <code>['BCD', 'ACD', 'ABD', 'ABC']</code>, not including the <code>1</code> part.</p>
  
  <p>it there an easy way to do this in python?</p>