Parsing arbitrary arguments using argparse

parsing.py

import sys
import argparse

parser = argparse.ArgumentParser()
parser.add_argument("--add_argument", help="Add argument for test subcommand",
        dest="ext_args", action="append")

subparsers = parser.add_subparsers(help="sub-command help")
test_parser = subparsers.add_parser("test", help="Test subcommand")

(kargs, xargs) = parser.parse_known_args()

for arg in kargs.ext_args:
    print(arg)
    test_parser.add_argument("--" + arg, "-" + arg, action="store_true")

(nkargs, _) = test_parser.parse_known_args(xargs)

print("nkargs:")
print(nkargs)