Check element exists in array
<p>In PHP there is the <code>isset()</code> thing <a href="http://au2.php.net/manual/en/function.isset.php" rel="nofollow">http://au2.php.net/manual/en/function.isset.php</a> to check if something exists. How about Python?
I need to use this on arrays since I get some expected "IndexError: list index out of range" sometimes.</p>

<p>I guess I <em>could</em> use try/catching, but that's a last revert.</p>
