Homebrew: Rollback from Python 3.7 to Python 3.6.5.x? A brew upgrade upgraded my system Python to Python 3.7. Unfortunately, Python 3.7 breaks other software I need to use (including but not limited to Ansible). I imagine these problems will be worked out in the next week or so, but in the meantime, I'd like to rollback to Python 3.6.5.x

A brew info python shows that previous versions are still installed and not purged:

➜ brew info python
python: stable 3.7.0 (bottled), HEAD
Interpreted, interactive, object-oriented programming language
https://www.python.org/
/usr/local/Cellar/python/3.6.5 (4,825 files, 100.8MB)
  Poured from bottle on 2018-03-31 at 20:21:57
/usr/local/Cellar/python/3.6.5_1 (4,788 files, 99.9MB)
  Poured from bottle on 2018-06-20 at 16:00:26
/usr/local/Cellar/python/3.7.0 (4,869 files, 103.3MB)
  Poured from bottle on 2018-07-01 at 19:30:37
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/python.rb


Various brew link and brew install commands that are suggested by other sites don't seem to work:

➜ brew link python@3.6.5
Error: No such keg: /usr/local/Cellar/python@3.6.5
➜ brew link python@3.6.5_1
Error: No such keg: /usr/local/Cellar/python@3.6.5_1
➜ brew install python@3.6.5
Error: No available formula with the name "python@3.6.5" 
==&gt; Searching for a previously deleted formula (in the last month)...
Error: No previously deleted formula found.
==&gt; Searching for similarly named formulae...
==&gt; Searching local taps...
Error: No similarly named formulae found.
==&gt; Searching taps...
==&gt; Searching taps on GitHub...
Error: No formulae found in taps.
If you still have the previous versions available, you can just use 

brew switch python 3.6.5_1