stream_with_context() might have missing type information

[hughsie]

On the LVFS we have the following code:

def _read_file_chunks(fn: str, chunksz: int = 0x80000) -> Iterator[bytes]:
    with open(fn, "rb") as fd:
        while 1:
            buf = fd.read(chunksz)
            if buf:
                yield buf
            else:
                break

Which is passed into a Response to achieve downloading chunking like this:

return Response(
    stream_with_context(_read_file_chunks(fullpath)),
    headers={
        "Content-Disposition": "attachment; filename={}".format(filename),
        "Content-Length": str(os.path.getsize(fullpath)),
    },
)

I think Iterator[bytes] is sane, according to https://mypy.readthedocs.io/en/stable/kinds_of_types.html#generators but mypy reports:

error: Argument 1 to "stream_with_context" has incompatible type "Iterator[bytes]"; expected "Union[Generator[Any, Any, Any], Callable[..., Any]]"

Perhaps stream_with_context() needs the additional Iterator[bytes] added to the Union[]?

Environment:

• Python version: 3.9.4
• Flask version: git@25884c4