Help understanding this piece of code
<p>The full source code is @ <a href="http://www.python.org/dev/peps/pep-0333/#the-server-gateway-side" rel="nofollow">PEP 333</a>. These two lines:</p>

<pre><code>status, response_headers = headers_sent[:] = headers_set
</code></pre>

<p>.. and ..</p>

<pre><code>headers_set[:] = [status, response_headers]
</code></pre>

<p>What am I looking at here? How does <code>[:]</code> differ from giving nothing at all (just <code>headers_set</code>)? If someone could provide an explanation, I'd be really glad.</p>
