Python Click: Error: Missing argument while calling the --help flag

Question

This is my code:

@click.group()
@click.pass_context
@click.argument('CHALLENGE', type=int)
def challenge(ctx, challenge):
    ctx.obj = Challenge(challenge=challenge)

@click.group(invoke_without_command=True, cls=PhaseGroup)
@click.pass_obj
@click.argument('PHASE', type=int)
def phase(ctx, phase):
    # Something

challenge.add_command(phase)

Together these commands are supposed to work like.

cli challenge 1 phase 1

Which works as intended by executing properly.

But when I use --help or define any other flags on phase, it throws

cli challenge 1 phase 1 --help

It throws Error: Missing argument "PHASE".

I searched SOF and found python click app is failing with indication of "missing argument" but cannot locate the issue This is a user who had the same issue, but I didn't quite understand the answer.

I cannot make the arguments optional since it is a crucial part of making the CLI work.

Answer 1

The fundamental problem your code is facing is that you are trying to use a group like a command. There are at least two ways to improve the situation:

Use a command:

The terminal enties are usually a click.Command not a click.Group. If you change phase to a click.Command the help will work as expected.

@challenge.command()
@click.argument('PHASE', type=int)
def phase(ctx, phase):
    ....    

Use no_args_is_help with the group:

If you pass no_args_is_help=True to the click.Group constructor, the help will be displayed as you hoped. But unless you have a really good reason for this I would instead suggest using a click.Command as shown above.

@challenge.group(invoke_without_command=True, no_args_is_help=True)
@click.argument('PHASE', type=int)
def phase(ctx, phase):
    ....

Side Note, you don't usually need add_command():

You do not generally need to use:

@click.command()
def my_command():
    ....
challenge.add_command(my_command)        

You can instead do:

@challenge.command()
def my_command():
    ....

Test Code:

import click

@click.group()
@click.pass_context
@click.argument('CHALLENGE', type=int)
def challenge(ctx, challenge):
    ctx.obj = challenge

@challenge.command()
@click.pass_obj
@click.argument('PHASE', type=int)
def phase1(ctx, phase):
    """Phase1 Command"""
    click.echo((phase))

@challenge.group(invoke_without_command=True, no_args_is_help=True)
@click.pass_obj
@click.argument('PHASE', type=int)
def phase2(ctx, phase):
    """Phase2 Group"""
    click.echo((phase))


if __name__ == "__main__":
    commands = (
        '--help',
        '1 phase1',
        '1 phase1 --help',
        '1 phase1 2 ',
        '1 phase1 2 --help',
        '1 phase2',
        '1 phase2 --help',
        '1 phase2 2 ',
        '1 phase2 2 --help',
        '--help',
    )

    import sys, time

    time.sleep(1)
    print('Click Version: {}'.format(click.__version__))
    print('Python Version: {}'.format(sys.version))
    for cmd in commands:
        try:
            time.sleep(0.1)
            print('-----------')
            print('> ' + cmd)
            time.sleep(0.1)
            challenge(cmd.split())

        except BaseException as exc:
            if str(exc) != '0' and \
                    not isinstance(exc, (click.ClickException, SystemExit)):
                raise

Test Results:

Click Version: 6.7
Python Version: 3.6.3 (v3.6.3:2c5fed8, Oct  3 2017, 18:11:49) [MSC v.1900 64 bit (AMD64)]
-----------
> --help
Usage: test.py [OPTIONS] CHALLENGE COMMAND [ARGS]...

Options:
  --help  Show this message and exit.

Commands:
  phase1  Phase1 Command
  phase2  Phase2 Group
-----------
> 1 phase1
Usage: test.py phase1 [OPTIONS] PHASE

Error: Missing argument "PHASE".
-----------
> 1 phase1 --help
Usage: test.py phase1 [OPTIONS] PHASE

  Phase1 Command

Options:
  --help  Show this message and exit.
-----------
> 1 phase1 2 
2
-----------
> 1 phase1 2 --help
Usage: test.py phase1 [OPTIONS] PHASE

  Phase1 Command

Options:
  --help  Show this message and exit.
-----------
> 1 phase2
Usage: test.py phase2 [OPTIONS] PHASE COMMAND [ARGS]...

  Phase2 Group

Options:
  --help  Show this message and exit.
-----------
> 1 phase2 --help
Usage: test.py phase2 [OPTIONS] PHASE COMMAND [ARGS]...

  Phase2 Group

Options:
  --help  Show this message and exit.
-----------
> 1 phase2 2 
2
-----------
> 1 phase2 2 --help
Usage: test.py phase2 [OPTIONS] PHASE COMMAND [ARGS]...

  Phase2 Group

Options:
  --help  Show this message and exit.
-----------
> --help
Usage: test.py [OPTIONS] CHALLENGE COMMAND [ARGS]...

Options:
  --help  Show this message and exit.

Commands:
  phase1  Phase1 Command
  phase2  Phase2 Group