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Don't map actual **kwargs to formal *args #6096

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Merged
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Dec 20, 2018
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Don't map actual **kwargs to formal *args #6096

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a823c6c
Don't map actual **kwargs to formal *args
JukkaL Dec 20, 2018
66ac3ea
Update test case
JukkaL Dec 20, 2018
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6 changes: 4 additions & 2 deletions mypy/argmap.py
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Original file line number Diff line number Diff line change
Expand Up @@ -81,8 +81,10 @@ def map_actuals_to_formals(actual_kinds: List[int],
no_certain_match = (
not formal_to_actual[fi]
or actual_kinds[formal_to_actual[fi][0]] == nodes.ARG_STAR)
if ((formal_names[fi] and no_certain_match)
or formal_kinds[fi] == nodes.ARG_STAR2):
if ((formal_names[fi]
and no_certain_match
and formal_kinds[fi] != nodes.ARG_STAR) or
formal_kinds[fi] == nodes.ARG_STAR2):
formal_to_actual[fi].append(ai)
return formal_to_actual

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18 changes: 18 additions & 0 deletions test-data/unit/check-kwargs.test
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Expand Up @@ -403,3 +403,21 @@ class A:
tmp/m.py:1: error: Unsupported operand types for + ("int" and "str")
main:2: error: Unexpected keyword argument "x" for "A"
tmp/m.py:3: note: "A" defined here

[case testStarArgsAndKwArgsSpecialCase]
from typing import Dict, Mapping

def f(*vargs: int, **kwargs: object) -> None:
pass

def g(arg: int = 0, **kwargs: object) -> None:
pass

d = {} # type: Dict[str, object]
f(**d)
g(**d) # E: Argument 1 to "g" has incompatible type "**Dict[str, object]"; expected "int"

m = {} # type: Mapping[str, object]
f(**m)
g(**m) # TODO: Should be an error
[builtins fixtures/dict.pyi]
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Maybe also add the second test case mentioned in the issue? The one with:

def b(arg: str='', **kw: int) -> None:
    pass

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@sobolevn sobolevn Nov 21, 2021 •
edited
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Three years later we have a similar error: #11583

But, calling b (in this case) with b(**{'x': 1}) will work in runtime. It will result in arg = '' (default value) and kw = {'x': 1}.
Not sure why this was explictly forbidden.

Do you remember why this was a problem?

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My PR with the alternative solution: #11589