Hydra: [Feature Request] Instantiate objects that require positional-only arguments

[NTL-Remi]

🚀 Feature Request

Hello,
I propose to add the ability to specify positional-only arguments for object instantiation.

Motivation

Is your feature request related to a problem? Please describe.
Since Python 3.8, and more precisely PEP 570, it is possible to define functions that forbid passing arguments by name.
From what I have seen from the docs and the code (call(), _instantiate_class() and _get_kwargs()) it is only possible to assign a dict-like structure to the params key in the YAML file, that will end up being passed as **kwargs, so there is currently no way to give positional-only arguments through config files.

Pitch

Describe the solution you'd like
Replacing the params key by args and kwargs, taking respectively a list and a dict.
This will be breaking existing code, so maybe keep params as an alias to kwargs.
I leave open the question of whether the pass-through args should append, prepend or override the config args.

Describe alternatives you've considered
On the user side, wrapping each class or function that needs it in an adapter class/function that takes the same arguments but without the positional-only restriction.
I can see that getting tedious, and it kind of defeats PEP 570 's purpose.

Are you willing to open a pull request? (See CONTRIBUTING) <= _btw, this link from the template is broken_
Maybe, if I have time.

[shagunsodhani]

Thanks for the feature request. One problem I see is that we support Python 3.6 and 3.7 as well while position arguments are only supported since Python 3.8

[remisphere]

Well 3.6 and 3.7 still accept positional arguments, they are just not mandatorily positional.
So regarding the python version, there is no backward compatibility problem.

[remisphere]

Sorry, I am the same person, just answering from another account ><

[shagunsodhani]

Oops :) I think I misunderstood the motivation. I assumed that you were requesting support for "positional-only" parameters.

[remisphere]

No, but from what I understand of the code, it is currently not possible to instantiate objects that have an __init__ with positional-only arguments.
From the config file at least.

[omry]

Thanks for the feature request.
The surface area of the instantiate method is already quite large and I am not sure this is worth the added complexity. Especially given that we plan to make the surface area even larger by supporting recursive instantiation (#566).

One workaround that you can employ now which is to use a static or class method as a factory, that will delegate the parameters appropriately for the underlying method.

I am going to keep it as a wishlist item, but this is not something that is likely to be added in the near future.
If this item gets many upvotes I may reconsider.

[omry]

Let's put a timeout of 12 months on this feature request. if there is no significant interest in 12 months I will close this.