install cv2 in python3 code example

Example 1: python install cv2

pip install opencv-python

Example 2: download cv2

pip3 install opencv-python for mac

Example 3: install opencv

sudo apt-get install libopencv-dev   # ubuntu c++

download required packages from below link:
https://docs.opencv.org/4.0.1/d7/d9f/tutorial_linux_install.html

NOTE: you can download required packages by "sudo apt-get install <packages>" or 
download source code by git using above link

tags: ubuntu, c++, opencv 4 version