Can't set the default value for multiple options with optional values

[ikapelyukhin]

The following example combines optional values with multiple options:

#!/usr/bin/env python3

import click


@click.command()
@click.option('--label', multiple=True, is_flag=False, flag_value='default')
def cli(label):
    print(label)
    print(f"click.core._flag_needs_value: {click.core._flag_needs_value}")


cli()

$ ./test.py --label --label test
('<object object at 0x7f5ef63ec250>', 'test')
click.core._flag_needs_value: <object object at 0x7f5ef63ec250>

Expected result: ('default', 'test')

Looks like when multiple=True, the sentinel value (click.core._flag_needs_value) is never substituted with the default value specified by flag_value.

Environment:

• Python version: 3.7.3
• Click version: 8.0.1

[janluke]

Is this thing of using an option both as a flag and a non-flag common practice? I've never seen something like that in the CLIs I've used. Personally I wouldn't even allow it.

[davidism]

Yeah, this doesn't seem like a feature we were intending to support. I'll probably close this, if someone wants to make a PR that makes it work consistently I'm open to it, but I don't think it needs to be an open issue.

[ikapelyukhin]

Is this thing of using an option both as a flag and a non-flag common practice?

It's probably rather uncommon, but it is something I've run into. And I'm not using it as a flag per se: in my (somewhat strange, I admit) use case it is possible to create a label without any text, so --label is basically a shorthand for --label "". This also happens to work perfectly fine when multiple=False.

Yeah, this doesn't seem like a feature we were intending to support.

Well, if it isn't supported then it would be nice to get an exception when conflicting options (is_flag=False and multiple=True) are specified. Otherwise you get '<object object at 0x7f5ef63ec250>' as the option value instead of the default, that doesn't seem like correct behavior.

I'll probably close this, if someone wants to make a PR that makes it work consistently I'm open to it, but I don't think it needs to be an open issue.

I can undo all changes related to prompting in #2004 for options with multiple values, then ParameterSource would be consistent.

[davidism]

We don't generally validate every single possible combination of things. There are a ton of combinations, and as a CLI application it has to be reasonably fast to create everything so it can execute when the user types the command.

I'm not clear why you want to roll back #2004, but you're welcome to do that if you want, just keep in mind our license.

[ikapelyukhin]

I'm not clear why you want to roll back #2004.

I don't mean the whole PR, I've made some changes that made things weird when it came to keeping ParameterSource consistent.

[ikapelyukhin]

OK, I've made the changes that I wanted, so #2004 is good to go from my perspective.