Why not reference python3 as just python too when installed from brew?

[programmer04]

Python has been removed from macOS default installation - check macOS Monterey 12.3 Release Notes. Python in version 2 reaches the end of life over two years ago at January 1, 2020. It shouldn't be used anywhere.

Thus my question is why not just install (link) the newest available python3 in homebrew-core as python? The same for having pip3 to be available as pip. I think it's more convenient and natural to just type python to use it. Linux distributions do it this way e.g. Fedora.

I'm creating this as a GH discussion, not a GH issue because maybe I'm missing some crucial context. Please let me know what you think

[carlocab]

I suggested this to @Homebrew/core a while back, and am still in favour of this (at least on macOS versions that do not include a /usr/bin/python).

I think there were reservations about breaking scripts that expect to find Python2 when they call python.

That said, those scripts are already broken. Maybe the error about python being missing would be more informative than the error you get when you try to run Python2 code in Python3.

[Bo98]

I think there were reservations about breaking scripts that expect to find Python2 when they call python.

It's not too rare of a scenario this. Ubuntu has a separate python-is-python3, for example.

I don't hold any particular opinion either way though. I'm fine with changing this if there's interest.

[programmer04]

Yeah, they have it like in Debian which always tries to be extremely backward compatible. Maybe this approach is something to consider...

But on the other hand, Arch does the same as Fedora. I'm in the camp that we should kill with fire any references to python2 anywhere to finish this painful transition from 2 to 3

[SMillerDev]

The python project actually has rules about this: https://peps.python.org/pep-0394/

[carlocab]

The python project actually has rules about this: https://peps.python.org/pep-0394/

This came up in the last discussion too. The only requirement relevant is that python better be what you get when you call python3, which is what is suggested here.

[programmer04]

Yeah @carlocab and PEP 394 was created almost ten years before EOL for Python 2 and the last modifications for allowing more flexibility were in 2019

[programmer04]

To sum up the discussion in the suggested answer started by @carlocab there are two options on the table

• link python3 to python and pip3 to pip on macOS Monterey 12.3 and newer during installation by default (like e.g. on Arch or Fedora)
• introduce to homebrew-core the new package python-is-python3 that purpose is only to link python3 to python and pip3 to pip (like e.g. on Debian), anybody who wants to have this behavior can just install it

Maybe we can have some discussion/voting here? Or should I move it to a GH issue for better visibility and more opinions?

[aristocrates]

Although it is helpful that the option exists right now to add $(brew --prefix)/opt/python/libexec/bin to $PATH, it would be great to have the option to manage this through brew itself:

• Managing my shell profile dotfile setup tends to be more work than installing packages with brew, and it also tends to be a lot more fragile.
  • In the context of explaining to other people how to do this (e.g. onboarding, stack exchange questions or similar, etc) brew install python-is-python3 would be a simpler and more reliable solution than formatting a properly escaped string to echo into the shell profile dotfile while keeping in mind that the desired destination dotfile differs by shell.
• brew manages the contents of $(brew --prefix)/opt/python/libexec/bin, and has complete control over whether that path is going to change or stop existing in the future. So it isn't ideal to have parallel references to it hard-coded into PATH set by a different system that brew has no knowledge of.

On the note of consistency, it seems like there is currently close to consensus in other package managers/distros/ecosystems that python = python3 is a standard if not canonical community convention. In modern releases, python 2 does not exist, and either command python points at python 3 by default as soon as python 3 is installed, or by default there is no command python but if you want to do so, you can make it point at python 3 through the package manager with one install command:

• the "official" python docker image links python to python3 https://github.com/docker-library/python/blob/69d5e5ca5a4323a79668573a8de02dc96fbc7f3b/Dockerfile-linux.template#L294-L301 - I'm aware this image is not maintained by the python developers
• https://packages.debian.org/bullseye/python-is-python3
• https://packages.ubuntu.com/focal/python-is-python3
• https://packages.fedoraproject.org/pkgs/python3.11/python-unversioned-command/

[aristocrates]

Case in point regarding fragility of opt-in via adding $(brew --prefix)/opt/python/libexec/bin to path: just around 10 days after I posted the above, having set up this workaround on a new machine with a fresh install, it already had broken on its own:

$ ls /opt/homebrew/opt/python/libexec/bin
ls: /opt/homebrew/opt/python/libexec/bin: No such file or directory

Root cause was of course things ending up in a weird state when switching to and linking python@3.11 and manually fixing that fixed the issue:

Warning: You have unlinked kegs in your Cellar.
Leaving kegs unlinked can lead to build-trouble and cause formulae that depend on
those kegs to fail to run properly once built. Run `brew link` on these:
  python@3.11

But $PATH of course had no idea that python was in a broken state and that /opt/homebrew/opt/python/libexec/bin didn't exist, because $(brew --prefix)/opt/python/libexec/bin was just hardcoded into shellenv dotfiles. And maybe one day that path stops existing not due to a bug or brew link gone wrong, but rather an intentional breaking change in how python and/or brew chooses to package python.

[MikeMcQuaid]

@aristocrates Try to use $(brew --prefix python) which will error out if Python isn't installed.

[aristocrates]

@MikeMcQuaid thanks, I made a PR to change the unversioned symlink note on https://docs.brew.sh/Homebrew-and-Python#python-3y since (at least with a typical setup with bash and .bash_profile) you get a visible error message when opening a shell if the package is not installed which is really helpful.

Homebrew/brew#14738

That said, this general class of failure modes still makes a good case for a python-is-python3 package:

• I'm not sure this would have fixed the particular case I ran into

  Does brew --prefix python error out when the package is installed but not linked (such as when there was an error during brew link during package upgrade)? I can't actually reproduce the state I was in before fixing this particular issue so I can't test directly what brew --prefix python would have said, but with brew unlink python@3.11 I still get no error with brew --prefix python nor with brew --prefix python@3.11

• This also doesn't mitigate the possibility that brew one day changes its organization of python executables. If there was a python-is-python3 package, any breaking changes with executables organization could ship at the same time as any adjustments needed on the python-is-python3 package's end.

[MikeMcQuaid]

Thanks for the PR @aristocrates, queued for merge now.

• but with brew unlink python@3.11 I still get no error with brew --prefix python nor with brew --prefix python@3.11

the opt link is resistant to brew unlink

• If there was a python-is-python3 package, any breaking changes with executables organization could ship at the same time as any adjustments needed on the python-is-python3 package's end.

This is something we'll consider 👍🏻