ubuntu16.04默认安装python3以上，需要手动安装2.7。
1、先确保make、gcc、g++已经安装好，如果没有则需要先安装这三个程序，均使用apt-get的方式直接装；
2、下载python2.7包：
wget https://www.python.org/ftp/python/2.7.13/Python-2.7.13.tgz
3、解压该包：
tar -xvf Python-2.7.13.tgz
4、进入该包：
cd Python-2.7.13
5、./configure
6、make
7、make install
安装完毕，如果因为权限问题失败，需要加sudo。
- sudo apt-get install 安装的package存放在 /usr/lib/python2.7/dist-packages目录中
- pip 或者 easy_install安装的package存放在/usr/local/lib/python2.7/dist-packages目录中
- 手动从源代码安装的package存放在site-packages目录中
The dist-packages is a Debian-specific convention that is also present in its derivatives, like Ubuntu. Modules are installed to dist-packages when they come from the Debian package manager into this location:
/usr/lib/python2.7/dist-packagesSince easy_install and pip are installed from the package manager, they also use dist-packages, but they put packages here:
/usr/local/lib/python2.7/dist-packagesFrom the Debian Python Wiki:
dist-packages instead of site-packages. Third party Python software installed from Debian packages goes into dist-packages, not site-packages. This is to reduce conflict between the system Python, and any from-source Python build you might install manually.
This means that if you manually install Python from source, it uses the site-packages directory. This allows you to keep the two installations separate, especially since Debian and Ubuntu rely on the system version of Python for many system utilities.
cv2:
pip install opencv-python
import cv2 出问题解决：
sudo ldconfig
http://blog.sina.com.cn/s/blog_4ddef8f80102v57b.html
http://www.cnblogs.com/world-for-gold/p/6837782.html
