title: Syntax behind sorted(key=lambda: ...)
body: <p>I don't quite understand the syntax behind the <code>sorted()</code> argument:</p>
  
  <pre><code>key=lambda variable: variable[0]
  </code></pre>
  
  <p>Isn't <code>lambda</code> arbitrary? Why is <code>variable</code> stated twice in what looks like a <code>dict</code>?</p>