One optional argument which does not require positional arguments

Question

I have a question regarding python\'s argparse: Is it possible to have a optional argument, which does not require positional arguments?

Example:

parser.         


        

Answer 1

• set a default value and nargs='?' for your positional arguments

• check manually in your code that both latitude and longitude have been set when you're not in list-methods mode

  parser = argparse.ArgumentParser()
  
  parser.add_argument('lat', help="latitude",default=None, nargs='?')
  parser.add_argument('lon', help="longitude",default=None, nargs='?')
  parser.add_argument('--method', help="calculation method (default: add)", default="add")
  parser.add_argument('--list-methods', help="list available methods", action="store_true")
  
  args = vars(parser.parse_args())
  
  if not args['list_methods'] and (args['lat'] == None or args['lon'] == None):
      print '%s: error: too few arguments' % sys.argv[0]
      exit(0)
  
  if args['list_methods']:
      print 'list methods here'
  else :
      print 'normal script execution'
  

which gives :

$ test.py --list-methods
list methods here

$ test.py 4
test.py: error: too few arguments

test.py 4 5
normal script execution