I have an Ubuntu 14.04 system, on which I want to install OpenCV and use it with Python 2.x.
I installed OpenCV using the instructions here: https://help.ubuntu.com/
For those who are trying to use 3.1.0 but after installing python says "cv2 module not found".
You likely have python but not python-dev.
sudo apt-get install python-dev
then reinstall 3.1.0 and it'll work.