I am adding subparsers to my parser to simulate subcommands functionality (for example code see: Simple command line application in python - parse user input?). Now I want to add a quit subparser/command that takes no arguments and has a "quit" action attached. Is it possible ? How can I go about it ?
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1 Answer
The documentation for subcommands gives two examples of how to identify the subparser.
https://docs.python.org/dev/library/argparse.html#sub-commands
One is to give the add_subparsers a dest:
def do_quit(args):
# action
quit()
parser = ArgumentParser()
subparser = parser.add_subparsers(dest='cmd')
....
subparser.add_parser('quit')
...
args = parser.parse_args()
print args.cmd # displays 'quit'
if args.cmd == 'quit':
do_quit(args)
the other is to use set_defaults to link the subparser with a function:
parser = ArgumentParser()
subparsers = parser.add_subparsers()
...
parser_quit = subparsers.add_parser('quit')
parser_quit.set_defaults(func=do_quit)
...
args = parser.parse_args()
args.func(args)
On further thought, here's a way, using a custom Action. It is like _HelpAction (which is used by a -h). It's called by a positional argument with nargs=0 (or '?'). Such an argument is always called, even though there are no strings to match it (or rather, 0 strings match it). This a logical, but somewhat obscure, consequence of how positionals are handled.
class QuitAction(argparse.Action):
def __call__(self, parser, *args, **kwargs):
parser.exit(message="QUITTING\n")
p=argparse.ArgumentParser()
sp=p.add_subparsers(dest='cmd')
p1=sp.add_parser('quit')
p1.add_argument('foo', action=QuitAction, nargs='?', help=argparse.SUPPRESS)
p.parse_args(['quit'])
producing (when run in Ipython):
QUITTING
An exception has occurred, use %tb to see the full traceback.
SystemExit: 0
6 Comments
Mr_and_Mrs_D
Thanks! If you have a look at the linked code: stackoverflow.com/questions/25332925/… you will see that I want the parsing to take place automatically - I do not want to add logic outside the parser. No other way ? Can I add a "quit" argument to the main parser (no
-quit that is) ? edit: github
hpaulj
Sure - a
ArgumentParser subclass that redefines parse_args. It would first call super().parse_args (or parse_known_args) and then perform the 'logic outside the parser'. Only you would know exactly what is hidden behind that method definition.hpaulj
I added a method using an optional postional argument.
Mr_and_Mrs_D
Thanks ! I already have a parse method - I can do that. Re: the nargs hack: how can I then prevent the
foo argument to show up in quit's help ?Mr_and_Mrs_D
Hmm - I get
usage: sync quit [-h] dummy sync quit: error: too few arguments in Python 2.7.8 (dummy is foo, sync is the prog) - EDIT: nargs='?' fixed that ! - you should edit your answer probably |
