[Python-Dev] Another update for PEP 394 -- The "python" Command on Unix-Like Systems

[Petr Viktorin]

On 2/14/19 9:56 AM, Petr Viktorin wrote:
> On 2/13/19 4:24 PM, Petr Viktorin wrote:
>> I think it's time for another review.
> [...]
>> Please see this PR for details and a suggested change: 
>> https://github.com/python/peps/pull/893
> 
> Summary of the thread so far.
> 
> Antoine Pitrou noted that the PEP should acknowledge that there are now 
> years of
> established usage of `python` as Python 3 for many conda users, often as 
> the "main" Python.
> 
> Victor Stinner expressed support for "python" being the latest Python 
> version, citing PHP, Ruby, Perl; containers; mentions of "python" in our 
> docs.
> 
> Steve Dower later proposed concrete points how to make "python" the 
> default command:
>    * our docs should say "python" consistently
>    * we should recommend that distributors use the same workaround
>    * our docs should describe the recommended workaround in any places 
> people are likely to first encounter it (tutorial, sys.executable, etc.)
> 
> Chris Barker added that "python3" should still be available, even if 
> "python" is default.
> 
> Barry Warsaw gave a +1 to making "python" default, noting that there 
> were plans to change this when Python 2 is officially deprecated. But 
> distros need to make decisions about 2020 now.
> 
> Chris Barker noted that users won't see any discuntinuity in 2020. 
> That's just a date support from CPython devs ends.
> 
> Victor pointed to discussions on 4.0 vs. 3.10. (I'll ignore discussions 
> on 4.0 in this summary.)
> Victor also posted some interesting info and links on Fedora and RHEL.
> There was a discussion on the PSF survey about how many people use 
> Python 3. (I'll ignore this sub-thread, it's not really about the 
> "python" command.)
> 
> Steve noted that the Windows Store package of Python 3 provides 
> "python", but he is still thinking how to make this reasonable/reliable 
> in the full installer.
> 
> Several people think "py" on Unix would be a good thing. Neil 
> Schemenauer supposes we would encourage people to use it over 
> "python"/"python2"/"python3", so "python" would be less of an issue.
> 
> Neil Schemenauer is not opposed to making "python" configurable or 
> eventually pointing it to Python 3.
> 
> Jason Swails shared experience from running software with a 
> "#!/usr/bin/env python" shebang on a system that didn't have Python 2 
> (and followed the PEP, so no "python" either). The workaround was ugly.

There haven't been many new ideas since this summary – mostly it was 
explaining and re-hashing what's been mentioned before.
Matthias Klose pointed out some Debian/Ubuntu points, to which I'll add 
the situation in other distros I know of.

*Debian* is concerned that python → python3 will break software
after an upgrade. Debian appears to not want to ship the unversioned 
command after py2 removal.

For *Ubuntu*, Matthias is not sure if he wants a python executable at 
all. He notes that pypi.org recommends pip, and pip still breaks 
system-installed packages when asked to.

For both Ubuntu 20.04 LTS and Debian bullseye, the goal is that distro 
packages don't use the unversioned shebang.

*Fedora* packages don't use the unversioned shebang. If it was up to me, 
the unversioned command would be removed in F31 (released in the first 
half of 2019) and then pointed to python3 in F32 (second half). But we'd 
rather happy to follow upstream consensus. (And the PEP, if it reflects 
the consensus.)

In *RHEL*, the unversioned command is missing by default. Sysadmins can 
change it, but are advised to use python2/python3 instead. RHEL decision 
makers don't give the PEP much weight.

*Arch* did the switch to python3 a long time ago (and the resulting fire 
wasn't all that bright).

With *Homebrew*, `python` points to Homebrew’s Python 2.7.x (if 
installed) otherwise the macOS system Python. That's exactly according 
to the PEP. They tried to switch python to python3 before, and got 
rather nasty backlash citing PEP 394. I assume they will follow the PEP 
quite strictly from now on.

The *macOS* system Python is out of our hands; Apple ignores upstream 
recommendations.