Looking to set a global default argument with argparse

Question

I am writting a new script and would like for the -h or --help argument to be called by default when the script is called without any parameters. So for example if someone calls command_line_utility.py then I want it to print the output you would get with command_line_utility.py -h.

I have dug around in the docs and looked at some examples, but all of them were specifying default argument values and not actually having arg parse call a default argument.

# Setting up Main Argument Parser
    main_parser = argparse.ArgumentParser(description="A set of python web utility scripts")
    main_parser.add_argument("-v",'--version', action='version', version='kuws V0.0.1')

    # Setting up the main subparser
    subparsers = main_parser.add_subparsers(help="Available commands found below, for more info on a command use: python command_line_utility.py <command> -h or kuws <command> -h")


    """Code below handles 'redirects' command in the main script
    i.e. >python command_line_utility.py redirects or kuws redirects
    """
    redirects_parser = subparsers.add_parser('redirects', argument_default='-u',
        help='Allows you to trace redirects and get other information')

    redirects_parser.add_argument('-u', "--url", 
        help='usage: python main.py redirects -u <url>; Lets you see the trace for a url', nargs='?', dest="trace_url")

As it stands when I run the file nothing actually gets printed to the command line. No help text or errors or anything.

Are you happy with the display when using the normal help command, the '-h' or '--help'? I don't see what a global default has to do with displaying the help. — hpaulj, Jun 23 '19 at 16:14
The command is going to be added to path and so for use ability I want the default to be -h so when people call the command they just see the help text instead of nothing. This is similar to how the git command works when you don't supply an argument. — Kieran Wood, Jun 24 '19 at 01:02
Nothing in your `parser` is required, so it doesn't raise an error. In older versions `subparsers` are required, now you have make that explicit. Others have show you can display a full `help` it there aren't any command line values. — hpaulj, Jun 24 '19 at 02:17
I don't think the `argument_default` parameter is doing anything useful for you. Normally the default for an argument is `None`. `argument_default` is just another way of changing that value (for all arguments of this subparser). More often we use the `default` parameter in the `add_argument` command. — hpaulj, Jun 24 '19 at 02:20

score 1 · Accepted Answer · answered Jun 23 '19 at 08:42

1

I'm afraid argparse doesn't have any built-in support for this, but you can identify this situation and print the help message:

import sys

if len(sys.argv)==1:
    parser.print_help(sys.stderr)
    sys.exit(1)

answered Jun 23 '19 at 08:42

Adam.Er8

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Francis Colas · Answer 2 · 2019-06-23T08:52:19.030

When using subparsers, a common scheme is using set_defaults(func=<function to be called>) and then calling this function (as explained in sub-commands).

You can simply define a first set_defaults(func=help) at first that will be overwritten with the functions of your command.

Note that you can also make the command required when you declare your subparsers (add_subparsers(..., required='True')) and thus, when the user invokes without a command, she will get an error with the usage.

score 0 · Answer 3 · answered Jun 23 '19 at 08:45

0

Checking that len(sys.argv)==1 and in that case calling the print_help method of the parser as described in this answer to a similar question is a possible way to print the help message defined in the parser when no arguments are given.

answered Jun 23 '19 at 08:45

Pete

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Looking to set a global default argument with argparse

3 Answers3