py3: add a bytes version of os.name os.name returns unicodes on py3. Most of our checks are like os.name == 'nt' Because of the transformer, on the right hand side we have b'nt'. The condition will never satisfy even if os.name returns 'nt' as that will be an unicode. We either need to encode every occurence of os.name or have a new variable which is much cleaner. Now we have pycompat.osname. There are around 53 occurences of os.name in the codebase which needs to be replaced by pycompat.osname to support Python 3.