title: Is there a way to set delimiter in python's argparse?
body: <p>I'm setting up argparser in python 3.6 and I need one of my arguments which defines range in the 2D plane to be in the format '-2.0:2.0:-1.0:1.0'.</p>
  
  <p>Which I tried to define as follows:</p>
  
  <pre><code>parser = argparse.ArgumentParser()  
  parser.add_argument('-r', '--rect', type=str, default='-2.0:2.0:-2.0:2.0', help='Rectangle in the complex plane.')
  args = parser.parse_args()
  
  xStart, xEnd, yStart, yEnd = args.rect.split(':')
  </code></pre>
  
  <p>unfortunately this results in
  <code>error: argument -r/--rect: expected one argument</code>
  after </p>
  
  <pre><code>python3 script.py --rect "-2.0:2.0:-2.0:2.0"
  </code></pre>
  
  <p>I'm looking for a way to get the 4 double numbers.</p>