Report an error if *args or **kwargs are passed when all other arguments are filled.
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Description
Bug Report
You can pass **kwargs or *args to a function, even if all of its arguments are already passed. I would expect this to raise an error, since it's only valid for empty kwargs and args.
To Reproduce
playground link
def f(x: int) -> int:
return x + 1
def g(x: int, **kwargs) -> int:
return f(x, **kwargs)
def h(x: int, args: list[int]) -> int:
return f(x, *args)
g(1, bar=42)
h(2, [])
h(3, [1337])
Expected Behavior
In both g and h, the x argument is specified, so I would expecting passing **kwargs or *args to produce an error, since they can never correctly pass additional arguments.
Actual Behavior
Success: no issues found in 1 source file
Your Environment
I tried several versions of mypy (including 1.16.0 and master) with python3.12 in mypy playground.
I tried with both with and without --check-untyped-defs
** Related Issues
- This is a more general case of https://github.com/python/mypy/issues/13380 (that issue specifically mentions functions with no arguments)
- https://github.com/python/mypy/issues/12206 is another issue with splatting, but I don't think it's quite the same
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the linked mypy playground reproduction and compare the behavior described for g and h. Review related issues 13380 and 12206 for existing context and scope. Done means mypy reports the invalid splatted-argument calls while preserving valid empty *args and **kwargs cases.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100