Generating a random string of fixed length where certain values are prohibited
<p>In Python 2.7, how do I most efficiently produce a unique, random string of <code>len=3</code> - formed only of digits - where values contained in a list (called <code>exclude_me</code>) are <em>not considered</em> while the random string is being calculated? </p>

<p>E.g. <code>exclude_me=['312','534','434','999',...........,'123']</code></p>