#!/usr/bin/env python
"""
Example of using python's argparse module to
offer a stand-alone option (e.g. extra help screen),
which will skip the required parameters (e.g. the filename).

Copyright (C) 2016 Assaf Gordon <assafgordon@gmail.com>
License: MIT
"""


import sys,argparse

class MoreHelpAction(argparse.Action):
    def __init__(self, option_strings, dest, **kwargs):
        super(MoreHelpAction, self).__init__(option_strings, '', nargs=0, **kwargs)

    def __call__(self, parser, namespace, values, option_string=None):
        text="""
This is an extra help screen.

Enjoy it...
"""
        print text
        sys.exit(0)


def parse_command_line():
    # Define parameters
    parser = argparse.ArgumentParser(
        formatter_class=argparse.RawDescriptionHelpFormatter,
        description="argparse example",
        epilog="""

Standard usage requires a filename,
but using --more-help will not.

Example:

    # Without a filename, usage error is reported:
    $ %(prog)s

    # with a filename, program runs:
    $ %(prog)s input.txt

    # with --more-help, a differet help script is show,
    # not requiring filename parameters
    $ %(prog)s --more-help

        """)


    # Add special action parameter
    parser.add_argument('--more-help', action=MoreHelpAction,
                        help="Additional information")



    # Positional parameter
    parser.add_argument('filename', metavar='FILE', help='file to process');
    args = parser.parse_args()

    return args


if __name__ == "__main__":
    args = parse_command_line()

    print "File to process:", args.filename