brew python3 suddenly stopped working on MacOs

Question

I had python (which was python2) and python3 both installed on my Mac OS High Sierra. I was doing some installations in which I ran:

brew install automake
brew install doxygen
brew install ant

and during these processes, my brew must have been updated as well. And now, I realised that python3 , which has been perfectly working for the last few months, just vanished.

> brew update
Already up-to-date.

> brew install python
Error: python 2.7.14 is already installed
To upgrade to 3.6.4_4, run `brew upgrade python`

> brew install python3
Error: python 2.7.14 is already installed
To upgrade to 3.6.4_4, run `brew upgrade python`

And now, I do not seem to be able to reinstall python3 back. What's, more, I am afraid that if I run brew upgrade python , I will lose access to python2.

PS : I've noticed the absence of python3 when I opened my terminal and it said:

Last login: Sat Mar 10 15:16:43 on ttys002
virtualenvwrapper_run_hook:12: no such file or directory: /usr/local/bin/python3
virtualenvwrapper.sh: There was a problem running the initialization hooks.

If Python could not import the module virtualenvwrapper.hook_loader,
check that virtualenvwrapper has been installed for
VIRTUALENVWRAPPER_PYTHON=/usr/local/bin/python3 and that PATH is
set properly.

Any ideas on how to fix this or what might have been the cause of the problem?

Answer 1

The reason is explained here: https://brew.sh/2018/01/19/homebrew-1.5.0/

I would suggest to add the new formula: brew install python@2

Running brew info python@2 you will get the location of the package installed:

/usr/local/Cellar/python@2/2.7.14_3

Keep in mind that python@2 is a "keg-only" formula, which means that it's not linked into /usr/local . At this point, depending on your needs you should force a link to it if necessary. Try first a --dry-run to understand what will happen:

brew link --force --dry-run python@2

If you do not want to run the brew link command, you always create a convenient symbolic link (you will have to keep the link updated in case you run an update of the formula):

ln -s ../Cellar/python@2/2.7.14_3/bin/python python2

Bottom line is that homebrew started considering python2 obsolete.

Answer 2

In case someone else is having the same problem, brew upgrade python does not break anything. I ran it and I still have access to Python 2 and additionally, I got Python 3. Also, all old libraries remain pre-installed