Extracting empty dictionary as parameter should not raise "Too many arguments"

[provinzio]

Bug Report

Unpacking a dictionary to a parameters list can raise an undesired Too many arguments for .... call-arg error when the dictionary is empty. Ignoring the error raises an "Unused "type: ignore" error.
Please see my MWE below.

To Reproduce

from typing import Type


class Abstract:
    def __init__(self, one):
        pass


class A(Abstract):
    pass


class B(Abstract):
    def __init__(self, one, two):
        pass


MyClass: Type[Abstract]
if 2 + 2 > 4:
    MyClass = A
    more_kwargs = {}
else:
    MyClass = B
    more_kwargs = {"two": "two"}

# call-arg: Too many arguments for "Abstract"
my_class = MyClass("one", **more_kwargs)

#mypy(error): Unused "type: ignore" comment
my_class = MyClass("one", **more_kwargs)  # type: ignore

Expected Behavior

mypy should see, that we are unpacking nothing into the parameters list and therefore should not raise an error.

Actual Behavior

Unrequired Too many arguments for .... call-arg error is raised.

Your Environment

• Mypy version used: 0.950
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):

[mypy]
python_version = 3.9
exclude = .*py.*env.*
disallow_incomplete_defs = True
no_implicit_optional = True
warn_redundant_casts = True
warn_unused_ignores = True
warn_return_any = True
show_error_codes = True
warn_unused_configs = True

• Python version used: 3.9.1
• Operating system and version: Windows 10

[a-reich]

I can’t reproduce this error: https://mypy-play.net/?mypy=latest&python=3.9&flags=check-untyped-defs%2Cwarn-unused-ignores&gist=2332fbe5db67c44543b5e4814d1073ef
Since you’re using a compound conditional to control how the names are assigned, I don’t think this will be able to work the way you want? Mypy doesn’t know which value more_kwargs has and needs to use a general dict type. It’s not just a “{}” literal that can be treated specially.

[provinzio]

I can not reproduce the error on mypy-play net either nor in a MWE github repo https://github.com/provinzio/mypy-call-arg-error with the CI. This does confuse me.

I am using Visual Studio Code and it's showing me the error there, stating mypy as the source.

Any idea where I can start looking to fix this?

EDIT: Running mypy main.py in the console does show the error, too.

main.py:27: error: Too many arguments for "A"  [call-arg]
Found 1 error in 1 file (checked 1 source file)

[hauntsaninja]

I think you have an older version of mypy installed somewhere. I think there were a couple different changes to kwargs behaviour somewhere in the v0.900 to v0.920 range