Add feature to forbid option be passed multiple times

For example:

@click.option("--string", type=click.STRING)
def echo(string):
    click.echo(string)

when running

echo --string=str1 --string=str2

it will print the second one. I would like to forbid passing it more than once.

[davidism]

I’m sticking with the current behavior. It allows overriding options defined earlier, which is useful when using alias in the shell or building up a list of args in Python. The behavior seems consistent with Python itself, where later assignment overrides earlier ones.

[dawranliou]

I found a work-around that is to turn on the multiple flag and check the option’s length, for example:

import click

@click.command()
@click.option("--string", multiple=True, type=click.STRING)
def echo(string):
    if len(string) > 1:
        raise click.exceptions.BadOptionUsage('--string', 'Only one --string option is allowed.')
    string = string[0]
    click.echo(string)

if __name__ == '__main__':
    echo()

Run it:

$ python cli.py --string=hi
hi
$ python cli.py --string=hi --string=hi2
Usage: issue_955.py [OPTIONS]

Error: Only one --string option is allowed.