title: Python: How to get all default values from argparse
body: <p>When module <code>optparse</code> is used, then I can get all default values for all command line arguments like this:</p>
  
  <pre><code>import optparse
  
  if __name__ == '__main__':
      parser = optparse.OptionParser(usage='pokus --help')
      parser.add_option("-d", "--debug", action='store_true', dest="debug",
                        default=False, help='Enabling debugging.')
      options, args = parser.parse_args()
      print(parser.defaults)
  </code></pre>
  
  <p>Since <code>optparse</code> is deprecated it is wise to rewrite your code to use <code>argparse</code> module. However I can't find any way how to get all default values of all command line arguments added to parser object:</p>
  
  <pre><code>import argparse
  
  if __name__ == '__main__':
      parser = argparse.ArgumentParser(usage='pokus --help')
      parser.add_argument("-d", "--debug", action='store_true', dest='debug',
                          default=False, help='Enabling debugging.')   
      args = parser.parse_args()
      # &lt;---- How to get default values for all arguments here?
      # Not: vars(args)
  </code></pre>
  
  <p>I want to get all default values when I run program with (<code>./app.py -d</code>) or without any command line argument (<code>./app.py</code>).</p>