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

[Matthias Klose]

On 13.02.19 16:24, Petr Viktorin wrote:
> PEP 394 says:
> 
>> This recommendation will be periodically reviewed over the next few
>> years, and updated when the core development team judges it
>> appropriate. As a point of reference, regular maintenance releases
>> for the Python 2.7 series will continue until at least 2020.
> 
> I think it's time for another review.
> I'm especially worried about the implication of these:
> 
> - If the `python` command is installed, it should invoke the same
>   version of Python as the `python2` command
> - scripts that are deliberately written to be source compatible
>   with both Python 2.x and 3.x [...] may continue to use `python` on
>   their shebang line.
> 
> So, to support scripts that adhere to the recommendation, Python 2
> needs to be installed :(

Debian's concern about pointing python to python3 is that it will break software
after an upgrade.  The current state seems is still the same that Debian doesn't
want to ship a python symlink after the Python2 removal.

For Ubuntu, I'm not sure if I want a python executable at all, because there is
not much progress in handling more than one python installation, so just using
python3 for the distro sounds fine.  pypi.org now recommends unconditionally
installing with pip, and pip is still happy to modify system installed packages
when asked, messing around with the distro packages.  But probably that kind of
users then install their own python symlink anyway.

For the Ubuntu 20.04 LTS release and the Debian bullseye release (maybe 2021), I
am trying to make sure that the python shebang isn't used by distro packages
anymore (either by removing python2 altogether, or by using the
python2/python2.7 shebangs).

Matthias