You made changes to _TemporaryFileCloser but urllib.response.addinfourl here is a subclass of _TemporaryFileWrapper. Now after your changes the .close() and .cleanup() operations work but the wrapper is still in an inconsistent state. It cannot be used as a context manager, and cannot be iterated. The wrapper proxies attribute access to the file handle so asking things like exc.mode, exc.seekable(), etc. will all fail.

The cleanest solution would be to change HTTPError to not subclass this thing at all... but that ship has sailed a long time ago.

Your change weakens _TemporaryFileCloser by allowing it to silently accept None in lieu of a file handle. This makes tempfile worse, I'm not convinced this is a good compromise.

Instead, since HTTPError is already a hack (and there was literally a comment about why it's hacky where the bug was created), I would just replace the hack with a different one: set fp to io.StringIO() if the passed fp is None. It's still not perfect but I feel that would be more robust.