How to use sub-commands along with optional positional arguments in argparse

Question

Below scripts prints an output as well as opens a webpage based on command line arguments.

 #main.py import os, numpy import argparse import webbrowser new=2 def main(): parser = argparse.ArgumentParser() parser.add_argument('-i','--input',type=str, help='Choose input') parser.add_argument('-d','--display',dest='disp',type=str, help='Opens a webpage', default=None) args = parser.parse_args() if args.input == 'infile': print('This is input file') if args.disp == 'openbrowser': url = "https://stackoverflow.com/" webbrowser.open(url,new=new,autoraise=True) if __name__=='__main__': main()

If I use the following command:

 python3 main.py --input infile --display openbrowser

The desired output is attained. But, I would like --display (ideally without any str ) to be parsed along with --input as a sub-command and not as a separate optional flag argument -d . The flag -display is only used if --input is used as the primary flag, and even --display should be optional in itself and shouldn't be obligatory.

So I would like the command line arguments to look like:

 python3 main.py --input infile --display

This prints This is input file and opens webpage in the browser. and

python3 main.py --input infile

This prints the output This is input file only

Answer 1

You're looking for the action='store_true' property on the argument specification. https://docs.python.org/3/library/argparse.html#action

 parser.add_argument('-d', '--display', dest='disp', action='store_true', help='Opens a webpage')

 #main.py import os, numpy import argparse import webbrowser new=2 def main(): parser = argparse.ArgumentParser() parser.add_argument('-i','--input',type=str, help='Choose input') parser.add_argument('-d','--display',dest='disp', action='store_true', help='Opens a webpage') args = parser.parse_args() if args.input == 'infile': print('This is input file') if args.disp: url = "https://stackoverflow.com/" webbrowser.open(url,new=new,autoraise=True) if __name__=='__main__': main()

Answer 2

This should be exactly what you are looking for.

In order to add subcommands you use the ArgumentParser.add_subparsers method which requires no parameters and returns an object that can create as many subcommands as you would like.

 import os, numpy import argparse import webbrowser new=2 def main(): parser = argparse.ArgumentParser() subparsers = parser.add_subparsers() input_parser = subparsers.add_parser("input") input_parser.add_argument('filename', help='path to file') args = parser.parse_args() input_parser.add_argument( '-d', '--display', dest='disp', action='stor_true', help='Opens a webpage' ) if 'filename' in args: print('This is input file') if args.disp: url = "https://stackoverflow.com/" webbrowser.open(url,new=new,autoraise=True) if __name__=='__main__': main()