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Incorrect result type for returns.curry.partial with keyword arguments for positional parameters #2191

@Nifacy

Description

@Nifacy

Bug report

What's wrong

When using returns.curry.partial, if you partially apply a positional parameter using a keyword argument, the resulting type is incorrect. Result type of callable allows passing the remaining arguments as positional, but this leads to a runtime error.

Example

def foo(x: int, y: int) -> None:
    ...

bar = returns.curry.partial(foo, x=1)
reveal_type(bar)
# => Mypy: "def (y: builtins.int)"
# => Expected: "def (*, y: builtins.int)"

bar(2)
# No errors from mypy, but got runtime error
# TypeError: foo() got multiple values for argument 'x'

How is that should be

In this scenario, the remaining parameters should be strictly keyword-only. The resulting type should reflect this restriction, and passing a positional argument should be flagged as an error at type checking time.

System information

  • python version: 3.13.4
  • returns version: 0.25.0
  • mypy version: 1.15.0

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