Just noticed that it's a different missing module... enum
File "C:/msys32/mingw32/lib/python2.7/site-packages/cryptography/exceptions.py", line 7, in <module>
from enum import Enum
ImportError: No module named enum
pip list on my win7 machine shows enum34 installed.
EDIT: This is the final fix....
pacman -S mingw-w64-i686-python2-enum
Now the NVS partition generator works.
Need to do these two things in win10, as it appear the requirements script doesn't work correctly on 10 with IDF v3.1.1
pacman -S mingw-w64-i686-python2-cryptography
pacman -S mingw-w64-i686-python2-enum