title: Fastest way to merge two deques
body: <p>Exist a faster way to merge two deques than this?</p>
  
  <pre><code># a, b are two deques. The maximum length 
  # of a is greater than the current length 
  # of a plus the current length of b
  
  while len(b):
    a.append(b.popleft())
  </code></pre>
  
  <p>Note that I'm not interested in preserving input deques, I'm only interested in having the merged one as fast as possible.</p>