Passing zero or variable number of values to Click.Option

Question

Suppose we have the following function, which has an optional parameter exclude, which is expected to be a list of strings:

@group.command()
@click.option(???)
def load(exclude = None):
    # ...

I want the user to be able to execute the script like so:

python script.py load --exclude one two three

or

python script.py load --exclude something

In which case, I would expect exclude to be ['one', 'two', 'three'] and ['something'], respectively. But I want the number of values in --exclude to be variable, including 0. I.e. The user should be able to execute

python script.py load

In which case exclude should be None (or [], does not matter).

How can I do that using click?

My only viable option so far is forcing the user to use

python script.py load --exclude "one two three"

and then calling exclude.split(), but something cleaner would be better.

Answer 1

It doesn't appear to be supported, in the way that you want, by Click:

According to the docs Multi Value Options must have the number of options provided as specified in nargs, so nargs=2 requires 2 values.

additionally, multiple options will not negate the need to pass the option multiple times.

Your most likely solution is to pass a string and split, although I haven't used Click too deeply, so someone may have a better solution.