HTTPResponse is not recognized as a subtype of typing.IO

[pkch]

From SO:

request = urllib.request.Request(get_file_url, headers=self.data_api_headers)

with urllib.request.urlopen(request) as response:
    with open(export_file_path, 'wb') as out_file:

        shutil.copyfileobj(response, out_file)

This fails with Argument 1 to "copyfileobj" has incompatible type "Union[HTTPResponse, BinaryIO]"; expected IO[Any] because HTTPResponse derives from io.BufferedIOBase, which (despite being a binary IO) does not derive from typing.BinaryIO (nor does io.RawIOBase; also io.IOBase does not derive from typing.IO).

When I attempted to derive them as I thought would make sense, I got errors because __enter__ and other methods are defined both in io.IOBase and in typing.BinaryIO.

Not sure how to solve it.

[ilevkivskyi]

I think this kind of problems could be solved by protocols. I have encountered many similar issues recently. I will probably submit a PR today or tomorrow.

(Note that extensive changes to typeshed may be required, replacing nominal types with corresponding protocols).

[JelleZijlstra]

The IO types are especially complicated; there are lots of different "file-like" types with subtly different sets of methods. Maybe somebody will need to spend the time to carefully review all file-like types in the standard library to come up with a good set of protocols.

[emmatyping]

This came up again in python/typeshed#2188 (comment) it seems.

[JelleZijlstra]

This seems like a typeshed bug, not a mypy bug.

[asottile]

I've copied this issue to typeshed: python/typeshed#2189