title: main() function doesn't run when running script
body: <p>Consider:</p>
  <pre><code>#! /usr/bin/python
  
  def main():
      print(&quot;boo&quot;)
  </code></pre>
  <p>This code does nothing when I try to run it in Python 3.3. No error or anything.</p>
  <p>What’s wrong?</p>
  <pre class="lang-none prettyprint-override"><code>gvim script
  chmod 775 script
  ./script
  </code></pre>