title: How do you delete an argument from a namespace
body: <p><strong>Question</strong>: Given an argparse parser instance with some arguments added, is there a way to delete/remove an argument defined for it?</p>
  
  <p><strong>Why</strong>: Considering the exemple below:</p>
  
  <pre><code>&gt;&gt;&gt;import argparse
  &gt;&gt;&gt;parser = argparse.ArgumentParser()
  &gt;&gt;&gt;parser.add_argument('--imagePath', action = "store", default = 'toto')
  _StoreAction(option_strings=['--imagePath'], dest='imagePath', nargs=None, const=None, default='toto', type=None, choices=None, help=None, metavar=None)
  &gt;&gt;&gt;args = parser.parse_args()
  &gt;&gt;&gt;args
  Namespace(imagePath='toto')
  &gt;&gt;&gt;parser.add_argument('--resultPath', action = "store", default = 'titi')
  _StoreAction(option_strings=['--resultPath'], dest='resultPath', nargs=None, const=None, default='titi', type=None, choices=None, help=None, metavar=None)
  &gt;&gt;&gt;args = parser.parse_args()
  &gt;&gt;&gt;args
  Namespace(imagePath='toto', resultPath='titi')
  </code></pre>
  
  <p>If we will, later in the script, change the value of the args.imagePath?</p>
  
  <p>I does not found a method for change the value, but if I can delete / remove the argument imagePath it could be possible to define again imagePath with a new value !</p>