ANN001 is fired when argument already set (mypy not complain in such case).

[actionless]

def function(param=False) -> int:
    if param:
        return 1
    return 0

$ ruff test_ruff.py
Found 1 error(s).
test_ruff.py:1:14: ANN001 Missing type annotation for function argument `param`

$ mypy test_ruff.py
Success: no issues found in 1 source file

[edgarrmondragon]

FWIW mypy does catch the missing annotation in strict mode:

$ mypy checkANN001.py --strict
checkANN001.py:1: error: Function is missing a type annotation for one or more arguments  [no-untyped-def]
Found 1 error in 1 file (checked 1 source file)

[actionless]

thanks for clarifying

i wonder, if it would make sense having such option as a separate check? (in a similar way how self or cls annotation checks were extracted out)

[charliermarsh]

It could make sense to turn this into a configuration setting, like allow_star_arg_any and mypy_init_return.

[actionless]

closing because it unlikely to be implemented in mypy:
https://stackoverflow.com/a/64500210/1850190