Put subparser command at the beginning of arguments

Question

I wanted to create an interface with argparse for my script with subcommands; so, if my script is script.py, I want to call it like python script.py command --foo bar, where command is one of the N possible custom commands.

The problem is, I already tried looking for a solution here on StackOverflow, but it seems like everything I tried is useless.

What I have currently is this:

parser = argparse.ArgumentParser()

parser.add_argument("-x", required=True)
parser.add_argument("-y", required=True)
parser.add_argument("-f", "--files", nargs="+", required=True)

# subparsers for commands
subparsers = parser.add_subparsers(title="Commands", dest="command")
subparsers.required = True

summary_parser = subparsers.add_parser("summary", help="help of summary command")

• If I try to run it with:

args = parser.parse_args("-x 1 -y 2 -f a/path another/path".split())

I got this error, as it should be: script.py: error: the following arguments are required: command.

• If, however, I run this command:

args = parser.parse_args("summary -x 1 -y 2 -f a/path another/path".split())

I got this error, that I shouldn't have: script.py: error: the following arguments are required: -x, -y, -f/--files.

• If I put the command at the end, changing also the order of arguments because of -f, it works.

args = parser.parse_args("-x 1 -f a/path another/path -y 2 summary".split())

• If I add the parents keyword in subparser, so substitute the summary_parser line with summary_parser = subparsers.add_parser("summary", help=HELP_CMD_SUMMARY, parents=[parser], add_help=False), then I got:

  • script.py summary: error: the following arguments are required: command when summary is in front of every other argument;
  • script.py summary: error: the following arguments are required: -x, -y, -f/--files, command when summary is at the end of the args.

My question is, how I have to setup the parsers to have the behaviour script.py <command> <args>? Every command shares the same args, because they are needed to create certain objects, but at the same time every command can needs other arguments too.

Answer 1

Creating another parser helped me getting what I wanted. The root parser should add all the optional arguments - and also have add_help=False, to avoid an help message conflict -, then another parser - parser2, with a lot of fantasy - will be created.

The second parser will have subparsers, and they all needs to specify as parents the root parser.

parser = argparse.ArgumentParser(add_help=False)

parser.add_argument() ...

parser2 = argparse.ArgumentParser()
subparsers = parser2.add_subparsers(title="Commands", dest="command")
subparsers.required = True

summary_parser = subparsers.add_parser("summary", parents=[parser])
summary_parser.add_argument("v", "--verbose", action="store_true")

# parse args
args = parser2.parse_args()

Now the output will be this:

usage: script.py [-h] {summary} ...

optional arguments:
  -h, --help  show this help message and exit

Commands:
  {summary}
    summary   For each report print its summary, then exit

usage: script.py summary [-h] -x X -y Y -f FILES [FILES ...] [-v]

optional arguments:
  -h, --help            show this help message and exit
  -x X
  -y Y
  -f FILES [FILES ...], --files FILES [FILES ...]
  -v, --verbose