class instantiation with multiple parameters

[hadipash]

Hello, I have a question on how I can instantiate a class that requires multiple parameters that determined during run time only?
I followed the example on Optimizer but can't figure out how I can expand it to multiple parameters:

# Example from the website
class Optimizer:
    def __init__(self, params: Iterable):
        self.params = params


class SGD(Optimizer):
    def __init__(self, params: Iterable, lr: float):
        super().__init__(params)
        self.lr = lr


if __name__ == '__main__':
    value = {
        "class_path": "SGD",
        "init_args": {
            "lr": 0.01,
        },
    }

    parser = ArgumentParser()
    parser.add_argument("--optimizer", type=Callable[[Iterable], Optimizer])
    cfg = parser.parse_args(["--optimizer", str(value)])
    init = parser.instantiate_classes(cfg)
    optimizer = init.optimizer([1, 2, 3])

Let's say I want to add one more parameter to SGD(params, weight, lr). How will the flow change?

class SGD(Optimizer):
    def __init__(self, params: Iterable, weight: float, lr: float):
...
parser.add_argument("--optimizer", type=Callable[[Iterable, float], Optimizer])

gives the following error:

usage: example.py [-h] [--optimizer OPTIMIZER]
example.py: error: Parser key "optimizer":
  Expected a dot import path string: SGD

Setting class_path to __main__.SGD produces another error:

usage: example.py [-h] [--optimizer OPTIMIZER]
example.py: error: Parser key "optimizer":
  Type typing.Callable[[typing.Iterable, float], __main__.Optimizer] expects a function or a callable class: Expected '__main__.SGD' to be a class that instantiates into callable or a subclass of False.. Got value: Namespace(class_path='__main__.SGD', init_args=Namespace(lr=0.01))

[mauvilsa]

Thank you for reporting!

This seems to be a bug in line:

jsonargparse/jsonargparse/_typehints.py

Line 891 in 826d786

return_type = typehint.__args__[1]

Should be instead return_type = typehint.__args__[-1].

[mauvilsa]

@hadipash would you be interested in contributing the fix?

[hadipash]

Interested, but can only start working on this issue in the middle of next week at the earliest, if it's ok.

[mauvilsa]

can only start working on this issue in the middle of next week at the earliest, if it's ok.

That is okay. The task should be simple. Possibly just that line that I referenced above and add a unit test.