title: Importing OpenCV - import cv2 or cv3, and why does the directory matter?
body: <p>I am trying to use OpenCV for Python 3 for the first time. To install, I simply typed "pip3 install opencv-python" into the terminal. When I do this, I see in Finder (I'm on a Mac), that in /usr/local/lib/python3.7/site-packages, I now have a new folder called "cv2". This is strange. Why isn't it cv3, as I used pip3? I do not know.</p>
  
  <p>When I try to import cv2 from python3, it says "No module named 'cv2'". Luckily <a href="https://stackoverflow.com/questions/19876079/opencv-cannot-find-module-cv2">StackOverflow already has a solution</a>: if I first change directories like: "cd /usr/local/lib/python3.7/site-packages" then I will be able to open cv2. <strong>I do not know why this step is necessary for OpenCV.</strong> I don't have to do this to "import numpy" for example; "numpy" does not care what directory I start from, and it is listed like just another module like cv2.</p>
  
  <p>Anyways, I change directory to site-packages, start python3, and I import cv2. Now there is a new error. This time cv2 is found, but it says: </p>
  
  <p>"from .cv2 import *<br>
  ModuleNotFoundError: No module named 'cv2.cv2'"</p>
  
  <p>For the record, I also have Python 2.7. If I try "cd /usr/local/lib/python2.7/site-packages" and then start Python 2.7, I can import cv2. This is ok, but I want to use OpenCV with Python3.</p>
  
  <p>Let me summarize.</p>
  
  <p>(1) How can I get cv2 or cv3 to import when I start from any directory? Is this ever possible?</p>
  
  <p>(2) How can I get cv3 for python3? cv2 seems to be problematic in python3 because because there is no "cv2.cv2"</p>