On my linux Mint, I have installed with spack environment modules, configured with autoloading and use them to load python extensions.
It happens that
spack install py-flake8
module load py-flake8
flake8

result in error:

File "/kubuntu/home/lcalori/spack/RCM_test/deploy/rcm08/install/linux-linuxmint18-x86_64/gcc-5.4.0/py-configparser-3.5.0-gyfsxqxnkenrlpaam7zqlk4zox7uq4yi/lib/python2.7/site-packages/configparser.py", line 12, in
from backports.configparser import (
ImportError: No module named backports.configparser

Googling around, I found:
https://pypi.python.org/pypi/backports/

It seems that, the proper__init__.py file is lacking from

lib/python2.7/site-packages/backports

It probably relates to setuptools deciding to not install as it is a namespace package,
as shown by the line in spack-build.out:

Skipping installation of /kubuntu/home/lcalori/spack/RCM_test/deploy/rcm08/install/linux-linuxmint18-x86_64/gcc-5.4.0/py-configparser-3.5.0-gyfsxqxnkenrlpaam7zqlk4zox7uq4yi/lib/python2.7/site-packages/backports/init.py (namespace package)

it seems a simple patch to setup.py can fix