how can I make subparsers be required? [duplicate]

Question

I would like to make sure at least one of the sub commands is selected. But there is no required option for add_subparsers() how can I enforce at least one subparser is selected?

Currently I did this to mimic the effect:

subparsers = parser.add_subparsers( title='sub commands', help='valid sub commands', ) subparser1 = subparsers.add_parser('subcmd1') subparser1.set_defaults(which_subcmd='subcmd1') subparser2 = subparsers.add_parser('subcmd2') subparser2.set_defaults(which_subcmd='subcmd2') parsedargs = parser.parse_args() if 'which_subcmd' not in parsedargs: parser.print_help()

But I want an official way to do this and make the help content display something like {subcmd1 | subcmd2}

Update:

according to @hpaulj, in 3.7 there is required option. But I want some work around can work in python 3.5 and 3.6

New enough versions have a required parameter, stackoverflow.com/questions/23349349/… — hpaulj
– hpaulj, Commented May 1, 2019 at 16:29
My old answer shows how to set the required attribute in older versions. Don't forget to set the dest as well. — hpaulj
– hpaulj, Commented May 1, 2019 at 17:24

adrtam · Accepted Answer · 2019-05-01 16:21:57Z

Instead of printing help, I would prefer to raise an error:

if which_subcmd not in parsedargs: msg = "Subcommands needed: subcmd1, subcmd2" raise argparse.ArgumentTypeError(msg)

This way is more consistent with other argparse errors. But just a matter of taste. I don't see anything wrong on your approach as long as you exit from your script after that print_help() statement.

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