Collecting cv2
Could not find a version that satisfies the requirement cv2 (from versions: )
No matching distribution found for cv2
初学Python，在安装cv2框架的时候，报以上错误，试了很多次 pip install cv2 依然无效，后来查阅了好多资料，总结下面的方法，安装了opencv后，里面包含了cv2框架。
If you are using python 2 you can install with pip:
pip install opencv-python
Or use the equivilent for python 3:
pip3 install opencv-python