> I assume you're talking about realpath() here ...

Yes, and so are you :) Let's move that discussion to issue9949 and/or PR 15287.

> I think os.chdir should raise an exception when passed a device path.

When the OS starts returning an error code for this case, we can start raising an exception. It might be worth reporting these cases though, as you're right that they don't seem to be handled correctly.