Optional non-argument as the default

[wsande]

Let's say I have a 'show fruit' command with a completer that produces this when I tab:

ID
================
1     apple
2     orange
3     banana
all   (show all fruit)

I want to be able to type 'show fruit [ENTER]' instead of 'show fruit all [ENTER]'. If I just type 'show fruit' with no argument, it should assume 'all'. So basically I want ID to be an optional argument. In my subcommand processing function, I can check whether ID is present [1, 2, 3,...] or None, and if None, I treat it as 'all'

I have read the docs but can't quite figure out how to do that.

With the code I have, if they just type 'show fruit [ENTER]' they get a message:

Usage: show fruit [-h] ID {} ...
Error: the following arguments are required: ID

[kmvanbrunt]

This can be done by using argparse features.

Add these parameters to your add_argument() call.
nargs=argparse.OPTIONAL
default='all'

I took your code from another discussion thread and added these arguments.

fruit_arg = parser_show_fruit.add_argument('fruit',  choices_provider=fruit_completer, metavar='ID',  descriptive_header='',
                                           help="enter a fruit ID or 'all'", nargs=argparse.OPTIONAL, default='all')

[wsande]

Thanks again! I did try this, but I ran into a problem with subcommands. I added color and price subcommands to show fruit.
With the nargs=argparse.OPTIONAL and default='all' added to the add_argument() call, I can now type show fruit, and it defaults to all.

(Cmd) show fruit
showing all fruit:
fruit #1: apple (Fuji)
fruit #2: orange(Mandarin)
fruit #3: banana (Chiquita)

But when I type show fruit 1, it gives me an error:

(Cmd) show fruit 1
Usage: show fruit [-h] [ID] {color, price} ...
Error: invalid choice: '1' (choose from 'color', 'price')
(Cmd) show fruit all
Usage: show fruit [-h] [ID] {color, price} ...
Error: invalid choice: 'all' (choose from 'color', 'price')

Without the extra arguments, show fruit 1 displays the description for a fruit (or all fruit)

(Cmd) show fruit 1
You chose fruit #1: apple (Fuji)
(Cmd) show fruit all
showing all fruit:
fruit #1: apple (Fuji)
fruit #2: orange(Mandarin)
fruit #3: banana (Chiquita)
(Cmd)

The modified code is below.

import cmd2
from typing import  List
import argparse

fruit_choices = {}
def fruit_completer(self) -> List[cmd2.CompletionItem]:
    global fruit_choices
    fruit_choices = {1:'apple (Fuji)', 2:'orange(Mandarin)', 3:'banana (Chiquita)', 'all':'(show all fruit)' }
    return [cmd2.CompletionItem(item_id, description) for item_id, description in fruit_choices.items()]

show_parser = cmd2.Cmd2ArgumentParser()
show_subparsers = show_parser.add_subparsers(title='subcommands', help='subcommand help')
parser_show_fruit = show_subparsers.add_parser('fruit', help='show fruit help')
fruit_arg = parser_show_fruit.add_argument('fruit',  choices_provider=fruit_completer, metavar='ID',  descriptive_header='',
                                           help="enter a fruit ID or 'all'", nargs=argparse.OPTIONAL, default='all')

# fruit_arg = parser_show_fruit.add_argument('fruit',  choices_provider=fruit_completer, metavar='ID',  descriptive_header='',
#                                            help="enter a fruit ID or 'all'")

show_fruit_subparsers = parser_show_fruit.add_subparsers(title='subcommands', help='subcommand help')
parser_show_fruit_color = show_fruit_subparsers.add_parser('color', help='Fruit Color')
parser_show_fruit_price = show_fruit_subparsers.add_parser('price', help='Fruit Price')

class SAMPLE_CLI(cmd2.Cmd):
    def __init__(self):
        super().__init__()

    def show_fruit(self, args):
        fruit_completer(self)
        if args.fruit == 'all':
            self.poutput("showing all fruit:")
            for fruit in list(fruit_choices.keys()):
                if fruit != 'all':
                    self.poutput("fruit #{}: {}".format(fruit, fruit_choices[fruit]))

        else:
            self.poutput("You chose fruit #{}: {}".format(args.fruit, fruit_choices[int(args.fruit)]))


    def show_fruit_color(self, args):
        fruit_completer(self)
        colors = {1: 'red', 2: 'orange', 3:'yellow'}
        if args.fruit == 'all':
            fruit_list = list(fruit_choices.keys())
        else:
            fruit_list = [int(args.fruit)]
        # the 'all' item causes a problem, because it's not a fruit and its key is not an integer.
        #  The try-except is a clunky way to work around this
        for fruit in fruit_list:
            if fruit != 'all':
                self.poutput("{} is {}".format(fruit_choices[int(fruit)], colors[fruit]))


    def show_fruit_price(self, args):
        fruit_completer(self)
        prices = {1: 1.57, 2: 0.95, 3: 0.58}
        if args.fruit == 'all':
            fruit_list = list(fruit_choices.keys())
        else:
            fruit_list = [int(args.fruit)]
        for fruit in fruit_list:
            if fruit != 'all':
                self.poutput("{} is {}".format(fruit_choices[int(fruit)], prices[fruit]))


    parser_show_fruit.set_defaults(func=show_fruit)
    parser_show_fruit_color.set_defaults(func=show_fruit_color)
    parser_show_fruit_price.set_defaults(func=show_fruit_price)


    @cmd2.with_argparser(show_parser)
    def do_show(self, args):
        func = getattr(args, 'func', None)
        if func is not None:
            func(self, args)
        else:
            self.do_help('show')

if __name__ == '__main__':
    import sys
    app = SAMPLE_CLI()
    sys.exit(app.cmdloop())