title: Unable to downgrade python version in macos using Homebrew
body: <p>Facing issues when trying to downgrade python version from 3.7.3 to 3.6.5_1. I have did lot of research before reaching to stackoverflow family and all of them were suggesting the same resolution steps that i have tried as below, but found no luck. I looking for the python 3.6.5_1 version because Python 3.7 is unsupported by Keras/TensorFlow and thus are not a good choice for OpenCV either:</p>
  <p>Option 1:</p>
  <p><code>brew unlink python</code></p>
  <p><code>brew install --ignore-dependencies https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb</code></p>
  <p><strong>Error: Calling Installation of python from a GitHub commit URL is disabled! Use 'brew extract python' to stable tap on GitHub instead.</strong></p>
  <p>Option 2:
  <code>brew switch python 3.6.5</code></p>
  <p><strong>Error: python does not have a version &quot;3.6.5&quot; in the Cellar.</strong></p>
  <p>after couple of tries I realized that it is problem with the git url that homebrew has it to get python 3.6.5_1 version and that would have changed or the commit url might not be the latest.</p>
  <p>macOS version : Catalina 10.15.6</p>
  <p>So seeking your guidance and suggestions on how to solve this problem. Also please let me know if missed any info that is required to post here(which could've helped in solving the problem)</p>
  <p>Thanks in advance</p>