Trying to type check a program using np.nditer using mypy 0.812 and 0.910 and numpy 1.21.1 fails complaining about missing dunder methods. Looking at https://github.com/numpy/numpy/blob/main/numpy/__init__.pyi#L767 and https://github.com/numpy/numpy/blob/main/numpy/__init__.pyi#L633 I believe the issue stems from the fact that the presence of __getattr__ does not automatically cover all dunders.

Adding the following to nditer stub (below __getattr__) allow the code to type check properly. I can make a PR with those changes and any other deemed relevant to improve nditer typing.

    def __enter__(self) -> nditer: ...
    def __exit__(
        self,
        exc_type: Optional[Type[BaseException]],
        exc_value: Optional[BaseException],
        traceback: Optional[TracebackType]
    ) -> Optional[bool]: ...
    def __iter__(self) -> Any: ...

Reproducing code example:

import numpy as np

a = np.nditer(np.zeros((2, 2, 2)))
with a:
    for b in a:
        pass

Error message:

Mypy output:

test.py:4: error: "nditer" has no attribute "__enter__"
test.py:4: error: "nditer" has no attribute "__exit__"
test.py:5: error: "nditer" has no attribute "__iter__" (not iterable)
Found 3 errors in 1 file (checked 1 source file)

NumPy/Python version information:

Python 3.9.1, Numpy 1.21.1, Mypy 0.812 or 0.910 (only tested version)