title: How to unpack result of `zip` which might be empty?
body: <p>I have a generator for tuples which I want to use like this:</p>
  
  <pre><code>def pairs():
      yield from [("key1", 2), ("key2", 4), ("key3", 6)]
  
  keys, values = zip(*pairs())
  </code></pre>
  
  <p>Works like a charm, but now <code>pairs()</code> can also yield nothing resulting in an expression equivalent to </p>
  
  <pre><code>keys, values = []
  </code></pre>
  
  <p>Is it possible to force the output of <code>zip</code> to have a given dimension in a nice single expression?</p>
  
  <p>What I'd like to have is something like this:</p>
  
  <pre class="lang-py prettyprint-override"><code>&gt;&gt;&gt; keys, values = magic_extender(zip(*pairs()), 2)
  &gt;&gt;&gt; keys, values
  ((), ())
  </code></pre>