Python mypy Type Hinting shutil.copyfileobj() has incompatible type “Union[HTTPResponse, BinaryIO]”; expected IO[Any]

Question

I'm getting the following mypy error for the code below. How can I properly cast the response object so that mypy is happy with me passing it to the shutil.copyfileobj method?

error:Argument 1 to "copyfileobj" has incompatible type "Union[HTTPResponse, BinaryIO]"; expected IO[Any]

The following code streams the response from a web request to a file.

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)

Answer 1

This was a bug in typeshed

the HTTPResponse stub didn't extend from BinaryIO and therefore wasn't considered a candidate for functions taking IO[bytes] -- this has been fixed

This fix should land in the next release of mypy (should be 0.620 if I'm guessing their version scheme correctly). Alternatively, you can run mypy with --custom-typeshed-dir to get the changes sooner