Downgrading Python to version 3.6.5_1 with Homebrew on Mac OS X (brew install python 3.6)

After running brew update; brew upgrade, brew updated python to version 3.7.x.x. When my code stopped working, I noticed that some of the 3rd party packages i use are not compatible Python 3.7.x.x yet. So i decided to revert to Python 3.6.5_1 the version that i am certain i will not have any troubles with.

I failed after trying to to revert to an older version using the usual method: brew install python@3.6.5_1 or: brew install python@3.6.5 or even: brew install python@3.6

After spending some time testing solutions i found the following posts that explained the situation to a great extent:

• https://apple.stackexchange.com/questions/329187/homebrew-rollback-from-python-3-7-to-python-3-6-5-x
• https://github.com/tensorflow/tensorflow/issues/25093

So, without further due, here is the solution:

First let’s ask brew to remove the links to the most recent python version, that brew installed automatically:

$ brew unlink python

Then let’s install the version 3.6.5_1 by directing brew to the suitable commit of the python brew formula on the Homebrew formulae repository. The commit ID for Python 3.6.5_1 Formula is: f2a764ef944b1080be64bd88dca9a1d80130c558. To avoid the issue with circular dependencies the flag –ignore-dependencies must be used:

$ brew install --ignore-dependencies https://raw.githubusercontent.com/Homebrew/homebrew-core/f2a764ef944b1080be64bd88dca9a1d80130c558/Formula/python.rb

Then let’s ask brew to create the links to the freshly installed version of python:

$ brew switch python 3.6.5_1

And finally and most crucially, to avoid having to do that again after running brew update; brew upgrade. Tell brew that you don’t want to update the python formula in the future:

$ brew pin python

You can allow brew to update python by simply reverting the previous action:

$ brew unpin python