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[conformance suite] Update an assertion in historical_positional.py to allow an optional error #2167

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[conformance suite] Update an assertion in historical_positional.py to allow an optional error #2167

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2 changes: 1 addition & 1 deletion conformance/tests/historical_positional.py
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Expand Up @@ -26,7 +26,7 @@ def f1(__x: int, __y__: int = 0) -> None: ...
def f2(x: int, __y: int) -> None: ... # E


def f3(x: int, *args: int, __y: int) -> None: ... # OK
def f3(x: int, *args: int, __y: int) -> None: ... # E?
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@sinon sinon Jan 31, 2026 •
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But mandating that type checkers should permit the f3 definition appears inconsistent with this comment. The x parameter of this function accepts keyword arguments, and comes before a parameter that uses the legacy convention for denoting positional-only parameters, so according to the portion of the spec quoted here I think type checkers should emit an error on it.

Can you call f3 with x as a keyword argument though? Won't you get SyntaxError: positional argument follows keyword argument? So is it maybe the case that you can't actually use x as keyword argument based on that constraint from it's positioning before positional arguments.

# > Consistent with PEP 570 syntax, positional-only parameters cannot appear
# > after parameters that accept keyword arguments. Type checkers should
# > enforce this requirement:

So this then does apply?

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@carljm carljm Jan 31, 2026

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You can call f3 with x as a keyword argument; you just can't do it while also providing any additional *args:

>>> def f3(x: int, *args: int, __y: int) -> None: ...
>>> f3(x=1, __y=2)

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@AlexWaygood AlexWaygood Jan 31, 2026 •
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I should probably add a comment above the definition of f3 clarifying this, since it's admittedly a little subtle



f3(3, __y=3) # OK
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