import argparse

args = argparse.ArgumentParser()
args.add_argument('-u','--url',help='',metavar='')

group = args.add_mutually_exclusive_group()
group.add_argument('-s','--scan',help='scan url',metavar='URL')

args = args.parse_args()

def main():
    if args.scan:
        print('hello')

if __name__ == '__main__':
    main()

group.add_argument('-s','--scan',help='scan url',action="store_true")

C:Temp>python "arg.py" -s
hello