Python argparse example?

Question

I'm trying to learn argparse in order to use it in my program, the syntax should be like this:

-a --aLong <String> <String>
-b --bLong <String> <String> <Integer>
-c --cLong <String>
-h --help

I have this code:

#!/usr/bin/env python
#coding: utf-8

import argparse

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Lorem Ipsum')
    parser.add_argument('-a','--aLong', help='Lorem Ipsum', required=False)
    parser.add_argument('-b','--bLong', help='Lorem Ipsum', required=False)
    parser.add_argument('-c','--cLong', help='Lorem Ipsum', required=False)
    parser.add_argument('-h','--help', help='Lorem Ipsum', required=False)
    parser.parse_args()

The question is, I read in the official doc, saw YouTube videos, etc, but I couldn't understand how can I determine the number of "sub-arguments" of the "main-argument"?

Example: myApp.py -b Foobar 9000, how can I set that -b must have two "sub-arguments", and how can I get the values, Foobar and 9000?

And another doubt, I know I can set an argument to be required or not, but I wanted to make my program only executes when at least one argument is passed, any of the four mentioned.

Maybe it's a stupid question, but sorry, I can't understand it, and hopefully there is someone here with "teacher powers" to explain it.

Answer 1

import argparse

# Use nargs to specify how many arguments an option should take.
ap = argparse.ArgumentParser()
ap.add_argument('-a', nargs=2)
ap.add_argument('-b', nargs=3)
ap.add_argument('-c', nargs=1)

# An illustration of how access the arguments.
opts = ap.parse_args('-a A1 A2 -b B1 B2 B3 -c C1'.split())

print(opts)
print(opts.a)
print(opts.b)
print(opts.c)

# To require that at least one option be supplied (-a, -b, or -c)
# you have to write your own logic. For example:
opts = ap.parse_args([])
if not any([opts.a, opts.b, opts.c]):
    ap.print_usage()
    quit()

print("This won't run.")

Answer 2

The key to this is to define a required, mutually exclusive group.

import argparse

# Use nargs to specify how many arguments an option should take.
ap = argparse.ArgumentParser()
group = ap.add_mutually_exclusive_group(required=True)
group.add_argument('-a', nargs=2)
group.add_argument('-b', nargs=3)
group.add_argument('-c', nargs=1)


# Grab the opts from argv
opts = ap.parse_args()

# This line will not be reached if none of a/b/c are specified.
# Usage/help will be printed instead.

print(opts)
print(opts.a)
print(opts.b)
print(opts.c)