Weird/different behaviour of obj.downcast::<PyIterator>() on Windows vs. MacOS and Linux

[samuelcolvin]

See pydantic/pydantic-core#367 and the associated failing test.

Effectively, obj.downcast::<PyIterator>().is_ok() is true on windows, but false on macos and linux, for the following input.

from collections import Sequence

class MySequence(Sequence):
    def __init__(self):
        self._data = [1, 2, 3]

    def __getitem__(self, index):
        return self._data[index]

    def __len__(self):
        return len(self._data)

input_value = MySequence()

Anyone have any idea why this is? Could this be a bug in pyo3 or cpython?

@davidhewitt any input would be great.

[davidhewitt]

For the record, follow up in #2913