title: Passing empty string to argparse
body: <p>I'm using <code>argparse</code> (Python 3.2). A parameter <code>mode</code> is defined simply as:</p>
  
  <pre><code>p.add_argument('--mode', dest='mode')
  </code></pre>
  
  <p>I want to call the program from the command line in such a way that parameter <code>mode</code> is set to an empty string; or at least to a single space <code>' '</code> (I can strip whitespace later).</p>
  
  <p>I tried to use (under Windows) <code>program_name --mode ""</code> and <code>program_name --mode " "</code>, but neither worked.</p>