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I have Python 3.8 and 3.9 installed via Homebrew:

~ brew list | grep python
[email protected]
[email protected]

I want to use Python 3.9 as my default one with python3 command. I tried the following:

~ brew switch python 3.9
Error: python does not have a version "3.9" in the Cellar.
python's installed versions: 3.8.6

I tried to uninstall Python and reinstall it, but it's used by other packages:

~ brew uninstall python
Error: Refusing to uninstall /usr/local/Cellar/[email protected]/3.8.6
because it is required by glib and php, which are currently installed.
You can override this and force removal with:
  brew uninstall --ignore-dependencies python

How can I use Python 3.9?

Robo Robok
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  • Check out this: https://stackoverflow.com/questions/18671253/how-can-i-use-homebrew-to-install-both-python-2-and-3-on-mac – Tom Oct 14 '20 at 23:28
  • @Tom Are you sure it applies here? Python 2 and Python 3 are separate packages. – Robo Robok Oct 14 '20 at 23:44
  • For me Brew was only addressing `python3` and would not add a `python` link. I had to go in and cut up my `.bashrc` and `.profile` to edit my `$PATH` which was getting mangled by some inserts, presumably from some earlier installs, and then add a `python` symlink to the `python3` that I wanted, alongside the `python3` symlink in `/opt/homebrew/bin`. – NeilG May 30 '22 at 02:10

3 Answers3

92

There is an Homebrew known issue related to side by side install of Python 3.8 / 3.9. To workaround, following commands should work for you:

brew unlink [email protected]
brew unlink [email protected]
brew link --force [email protected]

Re-opening your terminal or execute command rehash can be required to take account the change.

Jean-Pierre Matsumoto
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    Once followed the steps you described, it's ok to use `brew uninstall [email protected]` as it will be not have anymore dependencies? – NZisKool Apr 14 '21 at 08:57
  • Works for me without `--force` and console re-openning, at least `python3 --version` shows linked python version. – mrgloom Aug 02 '21 at 15:21
  • Also here is example where I have some problems after unlink / link https://stackoverflow.com/questions/68634761/env-python3-9-no-such-file-or-directory/68729295#68729295 – mrgloom Aug 10 '21 at 15:11
  • The third command resulted in this error message: `Error: Could not symlink bin/2to3 Target /usr/local/bin/2to3 already exists. You may want to remove it: rm '/usr/local/bin/2to3' To force the link and overwrite all conflicting files: brew link --overwrite [email protected]` I did that, and it worked – rturquier Sep 28 '21 at 16:06
  • It does not work for modern days... please disregard (I wish there is a modern day downvote button!) – Eric Chen Dec 31 '22 at 06:54
6

Use pyenv. It's a software that lets you switch between any and all Python versions installed on your system. To install pyenv, use the following code in the command-line:

curl https://pyenv.run | bash
exec $SHELL

Then find the name of the python version you want to switch to with this:

pyenv versions

And select it with this:

pyenv global <version-name>

In your case, it's most likely named 3.9.0.

Seth
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    Why wouldn't I want to install `pyenv` through Homebrew? – Robo Robok Oct 15 '20 at 07:56
  • The script above does install through Homebrew *and* sets it up to launch `pyenv` on bootup. @RoboRobok – Seth Oct 15 '20 at 14:56
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    How come? There's `brew install pyenv` for that :D – Robo Robok Oct 15 '20 at 15:18
  • Yes, but it also modifies the on-boot script, which `brew install` doesn't do. It just is less hassle. @RoboRobok – Seth Oct 15 '20 at 16:31
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    This doesn't work for me. After installing with "brew install pyenv" running "pyenv versions" only lists "system" despite me having 3.8, 3.9 and 3.10 installed via Homebrew too. – markshep Apr 01 '22 at 14:20
  • I previously installed python with Homebrew and had to remove it via "brew uninstall [email protected]". After that I installed a previous version via "pyenv install 3.8.6" and "pyenv versions" returned the correct version under "/Users/${USER}/.pyenv/version". – Hahnemann Jul 05 '22 at 03:28
4

Updated MacOs Monterrey

For who are facing this problem add the pyenv path to your ~/.zshrc shell file.

export PATH="/Users/username/.pyenv/shims:${PATH}"
eval "$(pyenv init --path)"

Run in the terminal:

source ~/.zshrc

Check it out:

python3 --version

From the issue on GitHub.

Navid Khan
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Everton Costa
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