title: Test if executable exists in Python?
body: <p>In Python, is there a portable and simple way to test if an executable program exists?</p>
  
  <p>By simple I mean something like the <code>which</code> command which would be just perfect. I don't want to search PATH manually or something involving trying to execute it with <code>Popen</code> &amp; al and see if it fails (that's what I'm doing now, but imagine it's <code>launchmissiles</code>)</p>