How does Python Click library handle options that are flags and True by default?

Question

I just stumbled upon a piece of code that defines a click option as such:

@click.option(
    "-s",
    "--status",
    default=True,
    is_flag=True,
    help="Show status",
)

Does this means that the status is True, unless the -s is supplied, in which case it will become False?

Remediless

Answer 1

For options that are both a flag and defaulted to True, specifying the option on the command line will set that option to False; while not specifying will give the default True.

Test Code:

import click    

@click.command()
@click.option(
    "-s",
    "--status",
    default=True,
    is_flag=True,
    help="Show status",
)
def main(status):
    click.echo('status: {}'.format(status))


if __name__ == "__main__":
    commands = (
        '',
        '-s',
        '--status',
        '--help',
    )

    import sys, time

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

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

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)]
-----------
> 
status: True
-----------
> -s
status: False
-----------
> --status
status: False
-----------
> --help
Usage: test.py [OPTIONS]

Options:
  -s, --status  Show status
  --help        Show this message and exit.

Sudhir

Answer 2

While the question is old, I just stumbled upon, having a similar question. And I found the answer rather incomplete. So here is what I found out.

Actually the code example makes no sense. When using default=True, you should always specify an extra for name of the variable, otherwise either the variable or the option has a reversed logic.

So, in the original example, if you want --status to be the default, re-write the code like this:

@click.option(
    "-n",
    "--no-status",
    "status"
    default=True,
    is_flag=True,
    help="Do not show status",
)
def main(status):
...

If you change an existing tool like this, you may also want to re-add --status as a documented obsolete option to stay compatible.

Ranunculaceous