Fleshed out arg parser based on examples from python.org

invoke_args.py

import argparse
import sys
from pprint import PrettyPrinter
pp = PrettyPrinter()

task1_parser = argparse.ArgumentParser()
task1_parser.add_argument('integers', metavar='N', type=int, nargs='+',
                   help='an integer for the accumulator')
task1_parser.add_argument('--sum', dest='accumulate', action='store_const',
                   const=sum, default=max,
                   help='sum the integers (default: find the max)')

task2_parser = argparse.ArgumentParser()
task2_parser.add_argument('integers', metavar='N', type=int, nargs='+',
                   help='an integer for the accumulator')
task2_parser.add_argument('--sum', dest='accumulate', action='store_const',
                   const=sum, default=max,
                   help='sum the integers (default: find the max)')

TASKS = {
    "MAIN": {},  # Pseudo task
    "task1": {
        "task": object(),
        "parser": task1_parser,
    },
    "task2": {
        "task": object(),
        "parser": task2_parser,
    }
}

TASK_ARGS_MAP = {
    "MAIN": {
        "start": 0,
        "end": None,
    }
}


def main():
    current_task = "MAIN"
    for a in sys.argv[1:]:
        if a in TASKS:
            task_idx = sys.argv.index(a)
            TASK_ARGS_MAP[current_task]["end"] = task_idx
            TASK_ARGS_MAP[a] = {
                "start": task_idx,
                "end": None,
            }
            current_task = a
    for task, opts in TASK_ARGS_MAP.items():
        if opts["end"] is None:
            opts["end"] = len(sys.argv)
        opts["argv"] = sys.argv[opts["start"] + 1:opts["end"]]
        try:
            opts["args"] = TASKS[task]["parser"].parse_args(opts["argv"])
        except KeyError:
            pass

    pp.pprint(TASK_ARGS_MAP)
    print(TASK_ARGS_MAP["task1"]["args"].accumulate(
            TASK_ARGS_MAP["task1"]["args"].integers))
    print(TASK_ARGS_MAP["task2"]["args"].accumulate(
            TASK_ARGS_MAP["task2"]["args"].integers))

main()

Run the above code with args similar to this:

$ python invoke_args.py task1 1 2 3 5 --sum task2 2 3 4
{'MAIN': {'argv': [], 'end': 1, 'start': 0},
 'task1': {'args': Namespace(accumulate=<built-in function sum>, integers=[1, 2, 3, 5]),
           'argv': ['1', '2', '3', '5', '--sum'],
           'end': 7,
           'start': 1},
 'task2': {'args': Namespace(accumulate=<built-in function max>, integers=[2, 3, 4]),
           'argv': ['2', '3', '4'],
           'end': 11,
           'start': 7}}
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