Installing opencv 3.3 in ubuntu 16.04 LTS

I used to have to compile the source code and do all the painful stuff.
but luckily, we don't have to do it anymore.

1. Fast way: pip install opencv-contrib-python

2. Slow and painful way: ok I will update and do it when I have time. But you certainly don't want it, do you?

let me know if you do want me to experience the pain again. If I get 10 comments, I'll do it.

P/s: I assume that you guys reading this are using python. For those who use C++, I don't have to teach you this, right?