fix: Add dummy __init__ to ParameterizedFunction

[hoxbro]

See holoviz/panel#7690

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 87.24%. Comparing base (031a4f4) to head (7d95935).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
param/parameterized.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1021      +/-   ##
==========================================
- Coverage   87.25%   87.24%   -0.02%     
==========================================
  Files           9        9              
  Lines        4928     4930       +2     
==========================================
+ Hits         4300     4301       +1     
- Misses        628      629       +1     

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[maximlt]

I don't understand :) Is there some reproducible code I could run to validate the issue and that it's fixed with this change? I haven't seen the error reported on Panel.

[hoxbro]

I created this environment: mamba env create --name "tmp_param" python="3.12" "holoviews pyright" --offline --yes

❯ pyright example.py
/home/shh/Downloads/example.py
  /home/shh/Downloads/example.py:3:14 - error: Expected 0 positional arguments (reportCallIssue)
1 error, 0 warnings, 0 informations

~/Downloads via 🅒 tmp_param
❯ cat example.py
import holoviews as hv

hv.extension("bokeh")

[maximlt]

Ok so here's a reproducer, type checking it with pyright shows that error, mypy doesn't complain.

class Base:
    def __init__(self, **params):
        pass

class FunctionBase(Base):

    # def __init__(self, *args, **kwargs):
    #     super().__init__(*args, **kwargs)

    def __new__(cls, *args, **kwargs) -> Any:
        inst = Base.__new__(cls)
        result = inst.__call__(*args, **kwargs)
        return result

    def __call__(self, *args, **kwargs):
        raise NotImplementedError

class SomeFunction(FunctionBase):
    def __call__(self, *args, **kwargs):
        return 1

SomeFunction('test')

Indeed, adding the dummy __init__ makes pyright happier (and doesn't affect mypy). Not super satisfied with a run time solution to a type checking problem, I asked on pyright's forum if there's another solution. Wait a little bit before merging please.

EDIT:

Ah yeah to explain a little, in Python __init__ is only called if __new__ returns an instance of the class, which is not the case with ParameterizedFunction. That's the sort of thing that doesn't make the life of type checkers easy (ours in turn!).

[hoxbro]

Is there any overhead? As far as I see init is never called because of new bypass it.

[maximlt]

Yes that's true, still weird no? Pyright's developer answered saying that annotating __new__ with a return type of Any (which I tried but saw no change) should work and was buggy at the moment in Pyright but will be fixed in the next release microsoft/pyright#9907 (comment).