Implementing two positional arguments using argparse's `add_subparsers` method

Question

I would like to get the following functionality while using the add_subparsers method of the argparse library and without using the keyword argument nargs:

$ python my_program.py scream Hello
You just screamed Hello!!
$ python my_program.py count ten
You just counted to ten.

I know I could do this:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument("cmd", help="Execute a command", action="store",
  nargs='*')
args = parser.parse_args()
args_list = args.cmd

if len(args.cmd) == 2:
    if args.cmd[0] == "scream":
        if args.cmd[1] == "Hello":
            print "You just screamed Hello!!"
        else:
            print "You just screamed some other command!!"

    elif args.cmd[0] == "count":
        if args.cmd[1]:
            print "You just counted to %s." % args.cmd[1]
        else:
            pass

    else:
        print "These two commands are undefined"

else:
    print "These commands are undefined"

But then when I do $ python my_program.py I lose that default arparse text that shows a list of arguments etc. .

I know there is an add_subparsers method of the argparse library that can handle more than one positional argument but I have not found a way to get it properly working. Could anyone show me how?

Answer 1

import argparse

def scream(args):
    print "you screamed "+' '.join(args.words)

def count(args):
    print "you counted to {0}".format(args.count)

parser = argparse.ArgumentParser()

#tell the parser that there will be subparsers
subparsers = parser.add_subparsers(help="subparsers")

#Add parsers to the object that was returned by `add_subparsers`
parser_scream = subparsers.add_parser('scream')

#use that as you would any other argument parser
parser_scream.add_argument('words',nargs='*')

#set_defaults is nice to call a function which is specific to each subparser
parser_scream.set_defaults(func=scream) 

#repeat for our next sub-command
parser_count = subparsers.add_parser('count')
parser_count.add_argument('count')
parser_count.set_defaults(func=count)

#parse the args
args = parser.parse_args()
args.func(args)  #args.func is the function that was set for the particular subparser

now run it:

>python test.py scream Hello World!  #you screamed Hello World!
>python test.py count 10             #you counted to 10