title: Issues installing OpenCV with Python 3 on macOS High Sierra
body: <p>I have tried to install opencv3 with homebrew on my mac. I have run: </p>
  
  <pre><code>$ brew install opencv3 --with-contrib --with-python3 --HEAD
  </code></pre>
  
  <p>When I enter this command, opencv is installed but it says:</p>
  
  <pre><code>Warning: opencv: this formula has no --with-contrib option so it will be ignored!
  Warning: opencv: this formula has no --with-python3 option so it will be ignored!
  Warning: opencv: this formula has no --HEAD option so it will be ignored!
  </code></pre>
  
  <p>I have noticed that opencv will work within python 2 but I would like it to work in python 3 as well.</p>
  
  <p>I am using python 3.6.</p>