About from __future__ import absolute_import

http://blog.csdn.net/caiqiiqi/article/details/51050800

https://docs.python.org/3/library/__future__.html

https://docs.python.org/2.5/whatsnew/pep-328.html

http://legacy.python.org/dev/peps/pep-0328/

https://stackoverflow.com/questions/7075082/what-is-future-in-python-used-for-and-how-when-to-use-it-and-how-it-works