Mark Hammond to the rescue:

Checkin 2.131 of posixmodule.c changed os.stat on Windows, so that
"/bin/" type notation (trailing backslash) would work on Windows to
be consistent with Unix.

However, the patch broke the simple case of: os.stat("\\")

This did work in 1.5.2, and obviously should!

This patch addresses this, and restores the correct behaviour.