Hello,

I'm trying to write a plugin for my paramclasses library. I already posted about it on gitter to ask a few questions (without answer at the moment).

I'm still trying to get to work on my library's typing issues whilst being a complete noob on the subject.

So I started by writing a logger-like dummy plugin which shows the called hooked with their args/kwargs (so that I understand the mechanisms a bit better), and trying to solve the signature problem.

1. Nonparamclass MWE: looks OK

Here's a MWE:

class A:
    def __init__(self, *args: object, **kwargs: object) -> None:
    """Takes anything at runtime but raises unless only 'foo' kwarg."""
        if args or list(kwargs) != ["foo"]:
            msg = "Only 'foo' kwarg is acceptable"
            raise ValueError(msg)

        self.foo = kwargs.get("foo")


A(bar="should fail")

I would like mypy to pick up the fact that the signature is in fact A(*, foo). The logger picks up this (filtered to keep only signature related hooks):
(removing the report hook):

[get_function_signature_hook] → ('builtins.list',), {}
[get_method_signature_hook] → ('builtins.list.__ne__',), {}
[get_function_signature_hook] → ('builtins.ValueError',), {}
[get_method_signature_hook] → ('builtins.dict.get',), {}
[get_method_signature_hook] → ('builtins.dict.get',), {}
[get_method_signature_hook] → ('builtins.object.__init_subclass__',), {}
[get_function_signature_hook] → ('mwe.A',), {}

Q1. Am I right to assume that I logically should use get_function_signature_hook with mwe.A for this example?If so, I think this works fine since I have a way to write a plugin to do what I want.

Now on to my use case

2. Paramclass MWE: not OK

My usecase MWE would be:

from paramclasses import ParamClass


class A(ParamClass):
    foo: int


A(bar="should fail")

When I filter out the logger plugin output, to keep only the "signature" hook, I only get this which refers to internals that seem unrelated:

[get_function_signature_hook] → ('paramclasses.paramclasses._MissingType',), {}
[get_function_signature_hook] → ('paramclasses.paramclasses._run_once',), {}
[get_function_signature_hook] → ('paramclasses.paramclasses._run_once',), {}
[get_function_signature_hook] → ('paramclasses.paramclasses._run_once',), {}

So in the end, I'm completely lost on what I should/could do.

Q2. Is there a way to think about understanding the problem? Note that if useful, the __signature__ attribute returns the desired result at runtim.

Thanks in advance!
Élie