python
Dict unpacking type checks don't consider **kwargs
Bug Report:
In the below example (playground gist), mypy behaves differently with respect to **kwargs:
def func(x: bool = False, **kwargs):
print(x, kwargs)
# This is accepted by mypy.
func(y="y")
# This is flagged by mypy.
data = {"y": "y"}
func(**data)
The error is Argument 1 to "func" has incompatible type "**dict[str, str]"; expected "bool" [arg-type]. This is incorrect because the function has **kwargs, so the dict / function call should be considered type correct.
Your Environment:
- Mypy version used: latest (1.11.1)
- Mypy command-line flags: -
- Mypy configuration options from
mypy.ini(and other config files): - - Python version used: 3.12
Some related issues:
- https://github.com/python/mypy/issues/15317
- https://github.com/python/mypy/issues/5382
I have overlooked that data may specify x.
def func(x: bool = False, **kwargs):
print(x, kwargs)
data = {"x": "a"}
func(**data) # warning
Since mypy has no way to know the content of the dictionary (unless it's a TypedDict or frozendict), it is correct to flag this function call.
If func only expects strings, mypy accepts this.
def func(x: str = "text", **kwargs):
print(x, kwargs)
data = {"x": "a", "y": "b"}
func(**data) # ok
It also accepts this if x is explicitly provided.
def func(x: bool = False, **kwargs):
print(x, kwargs)
data = {"y": "b"}
func(x=True, **data) # ok