Improve error messages for unexpected keyword arguments in overloaded functions #20592
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JukkaL
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Jan 16, 2026
| def f(foobar: Union[int, str]) -> None: | ||
| pass | ||
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| f(fobar=1) # E: Unexpected keyword argument "fobar" for overloaded function "f" defined on line 4; did you mean "foobar"? |
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Don't report the line number here. It could be useful to report it, but we generally use a note, since the function could be in a different file so line number by itself isn't sufficient.
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That's a good point, I'll exclude the line number from the error messaging
| pass | ||
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| f(fobar=1) # E: Unexpected keyword argument "fobar" for overloaded function "f" defined on line 4; did you mean "foobar"? | ||
| f(random=[1,2,3]) # E: Unexpected keyword argument "random" for overloaded function "f" \ |
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Additional test ideas:
- Test multiple invalid keyword arguments
- Test both invalid keyword argument and incompatible positional argument
- Test both valid an invalid keyword arguments in the same call
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Diff from mypy_primer, showing the effect of this PR on open source code: prefect (https://github.com/PrefectHQ/prefect)
+ src/prefect/futures.py:223: error: Unexpected keyword argument "_sync" for overloaded function "result" of "State" [call-overload]
+ src/prefect/utilities/engine.py:764: error: Unexpected keyword argument "_sync" for overloaded function "result" of "State" [call-overload]
+ src/prefect/task_engine.py:529: error: Unexpected keyword argument "_sync" for overloaded function "result" of "State" [call-overload]
scipy (https://github.com/scipy/scipy)
+ scipy/sparse/linalg/tests/test_interface.py:306: error: Unexpected keyword argument "axis" for overloaded function "__call__" of "_GUFunc_Nin2_Nout1" [call-overload]
+ scipy/sparse/linalg/tests/test_interface.py:307: error: Unexpected keyword argument "axis" for overloaded function "__call__" of "_GUFunc_Nin2_Nout1" [call-overload]
xarray (https://github.com/pydata/xarray)
+ xarray/tests/test_plot.py:1167: error: Unexpected keyword argument "start" for overloaded function "arange" [call-overload]
+ xarray/tests/test_plot.py:1168: error: Unexpected keyword argument "start" for overloaded function "arange" [call-overload]
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This PR improves error messages when calling overloaded functions with unexpected keyword arguments, making it easier to identify and fix typos.
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