How to make python argparse mutually exclusive group arguments without prefix?

Question

Python2.7 argparse only accepts optional arguments (prefixed) in mutually exclusive groups:

parser = argparse.ArgumentParser(prog='mydaemon') action = parser.add_mutually_exclusive_group(required=True) action.add_argument('--start', action='store_true', help='Starts %(prog)s daemon') action.add_argument('--stop', action='store_true', help='Stops %(prog)s daemon') action.add_argument('--restart', action='store_true', help='Restarts %(prog)s daemon') 

$ mydaemon -h

usage: mydaemon [-h] (--start | --stop | --restart)  optional arguments:   -h, --help  show this help message and exit   --start     Starts mydaemon daemon   --stop      Stops mydaemon daemon   --restart   Restarts mydaemon daemon 

Is there a way to make argparse arguments behaves like traditional unix daemon control:

(start | stop | restart) and not (--start | --stop | --restart) ? 

Answer 1

from pymotw

import argparse  parser = argparse.ArgumentParser()  group = parser.add_mutually_exclusive_group() group.add_argument('-a', action='store_true') group.add_argument('-b', action='store_true')  print parser.parse_args() 

output:

$ python argparse_mutually_exclusive.py -h   usage: argparse_mutually_exclusive.py [-h] [-a | -b]  optional arguments:     -h, --help  show this help message and exit     -a     -b    $ python argparse_mutually_exclusive.py -a   Namespace(a=True, b=False)  $ python argparse_mutually_exclusive.py -b   Namespace(a=False, b=True)  $ python argparse_mutually_exclusive.py -a -b   usage: argparse_mutually_exclusive.py [-h] [-a | -b]   argparse_mutually_exclusive.py: error: argument -b: not allowed with argument -a 

version2

import argparse  parser = argparse.ArgumentParser()  subparsers = parser.add_subparsers(help='commands')  # A list command list_parser = subparsers.add_parser('list', help='List contents') list_parser.add_argument('dirname', action='store', help='Directory to list')  # A create command create_parser = subparsers.add_parser('create', help='Create a directory') create_parser.add_argument('dirname', action='store', help='New directory to create') create_parser.add_argument('--read-only', default=False, action='store_true',                        help='Set permissions to prevent writing to the directory',                        )  # A delete command delete_parser = subparsers.add_parser('delete', help='Remove a directory') delete_parser.add_argument('dirname', action='store', help='The directory to remove') delete_parser.add_argument('--recursive', '-r', default=False, action='store_true',                        help='Remove the contents of the directory, too',                        )  print parser.parse_args(['list', 'a s d', ]) >>> Namespace(dirname='a s d') print parser.parse_args(['list', 'a s d', 'create' ]) >>> error: unrecognized arguments: create 

Answer 2

For all the abilities and options in argparse I don't think you'll ever get a "canned" usage string that looks like what you want.

That said, have you looked at sub-parsers since your original post?

Here's a barebones implementation:

import argparse  parser = argparse.ArgumentParser(prog='mydaemon') sp = parser.add_subparsers() sp_start = sp.add_parser('start', help='Starts %(prog)s daemon') sp_stop = sp.add_parser('stop', help='Stops %(prog)s daemon') sp_restart = sp.add_parser('restart', help='Restarts %(prog)s daemon')  parser.parse_args() 

Running this with the -h option yields:

usage: mydaemon [-h] {start,stop,restart} ...  positional arguments:   {start,stop,restart}     start               Starts mydaemon daemon     stop                Stops mydaemon daemon     restart             Restarts mydaemon daemon 

One of the benefits of this approach is being able to use set_defaults for each sub-parser to hook up a function directly to the argument. I've also added a "graceful" option for stop and restart:

import argparse  def my_stop(args):     if args.gracefully:         print "Let's try to stop..."     else:         print 'Stop, now!'  parser = argparse.ArgumentParser(prog='mydaemon')  graceful = argparse.ArgumentParser(add_help=False) graceful.add_argument('-g', '--gracefully', action='store_true', help='tries to terminate the process gracefully') sp = parser.add_subparsers() sp_start = sp.add_parser('start', help='Starts %(prog)s daemon') sp_stop = sp.add_parser('stop', parents=[graceful],                     description='Stops the daemon if it is currently running.',                     help='Stops %(prog)s daemon') sp_restart = sp.add_parser('restart', parents=[graceful], help='Restarts %(prog)s daemon')  # Hook subparsers up to functions sp_stop.set_defaults(func=my_stop)  # Uncomment when my_start() and  # my_restart() are implemented # # sp_start.set_defaults(func=my_start) # sp_restart.set_defaults(func=my_restart)  args = parser.parse_args() args.func(args) 

Showing the "help" message for stop:

$ python mydaemon.py stop -h usage: mydaemon stop [-h] [-g]  Stops the daemon if it is currently running.  optional arguments:   -h, --help        show this help message and exit   -g, --gracefully  tries to terminate the process gracefully 

Stopping "gracefully":

$ python mydaemon.py stop -g Let's try to stop...