title: Default value of commandline parameters when no value is provided
body: <p>I am using ArgParse for giving commandline parameters in Python.</p>
  
  <pre><code>import argparse
  parser = argparse.ArgumentParser()
  parser.add_argument("--quality", type=int,help="enter some quality limit")
  args = parser.parse_args()
  qual=args.quality
  
  if args.quality:
    qual=0
  
  $ python a.py --quality 
  
  a.py: error: argument --quality: expected one argument
  </code></pre>
  
  <p>In case of no value provided,I want to use it as 0,I also have tried to put it as "default=0" in parser.add_argument,and also with an if statement.But,I get the error above.</p>
  
  <p>Basically,I want to use it as a flag and give a default value in case no value is provided.</p>