Ability to create mutually exclusive option groups.

[robhague]

Perhaps I'm missing something, but I can't find a way to create mutually exclusive option groups in Click. For example, I have a command that can take input from either a socket or a file, and I'd like the following syntax:

cmd [-file <filename> | -stream <address>] ...

At most one (or, in other examples, exactly one) of the options may be specified. Specifying more than one is a parse error caught by the library.

Is it possible to implement this in click at present? If not, would it be feasible to add it? I've not quite got my head around the general architecture yet. Would this feature be a reasonable fit, or does it go against the overall design in some way I've missed?

[hartror]

This is something I'd like as well which is currently not supported.

Perhaps it could look something like this:

@click.command()
@click.option_group(Option('-file'), Option('-stream'))
def command(file=None, stream=None):
    pass

Or perhaps option group could allow for mutally inclusive options, i.e -foo must be called with -bar. Inclusive seems the sensible default so there could be a param for exclusive such as:

@click.option_group(Option('-file'), Option('-stream'), exclusive=True)

@mitsuhiko thoughts? I'd be happy to put together a PR for this feature.

[ryanneufeld]

+1

[mitsuhiko]

I don't really see how this works from an API point of view. I would rather see some sort of post validation utility that can check that only one is set or something.

Definitely a strong -1 on the option_group thing.

[hartror]

post validation utility

Not clear on what you mean @mitsuhiko, "utility" in the context of click appears to mean methods like click.echo? If this is the case how would this allow click to generate a useful help message on --help?

More than happy for you to suggest an API for me to go implement and submit a PR.

[mitsuhiko]

Not clear on what you mean @mitsuhiko, "utility" in the context of click appears to mean methods like click.echo? If this is the case how would this allow click to generate a useful help message on --help?

Pretty much yes. I don't see how click would generate a nice looking help page for such things anyways. This gets too complex quickly. For instance some options might only conflict in relation to a specific setting of another option.

[nchammas]

I'm with @mitsuhiko in that I'm not sure how this would work in Click, but for what it's worth I have a similar use case.

The full use case is described in #329, but more simply: I have a tool that launches stuff into various cloud providers like AWS, GCE, and so forth. The choice of provider is an option.

Depending on what --provider is chosen, additional provider-specific options are required.

Personally, I don't care that the help page capture these kinds of dependencies between options. (e.g. If --provider is set to ec2, then --ec2-region must be specified.)

I care more that the dependency be captured in the parser (or perhaps in some nice utility method) and that helpful error message be provided.

My use case is quite complex, though. Perhaps it is a symptom of a complex design that Click shouldn't try to support.

[alanhamlett]

@nchammas have you found a solution for dynamically making --ec2-region a required option?

[nchammas]

@alanhamlett - Not yet, but when I have the time I am planning to write a utility function that captures simple dependencies like this. If it works well for my use case I will post it here as a proposed solution to this issue.

[alanhamlett]

I just used a callback function for now:
wakatime/wakadump@fc88de6

[alexandre-mbm]

👍

[mitsuhiko]

I'm going to close this. There is no likely API for this and you can already manually check on this in callbacks.

[alexandre-mbm]

you can already manually check on this in callbacks

I don't know if we are talking about the same thing, I don't understand as I use callback functions to create mutually exclusive option groups, and I am not familiar with the click's code, but I have rehearsed the following code for my project:

https://github.com/OSMBrasil/paicemana/blob/master/paicemana/clickexclusive.py