I think this is reasonable. Thanks for making the rationale clear! On Fri, Apr 12, 2019 at 8:02 AM Petr Viktorin <encu...@gmail.com> wrote:
> On 4/12/19 4:53 PM, Miro Hrončok wrote: > > Hello. > > > > Based on discussions in [1], Petr Viktorin and me have drafted a new > > update [2] to the PEP 394 (The "python" Command on Unix-Like Systems). > > > > The update gives distributors the opportunity to decide where does the > > "python" command lead to, whether it is present etc. > > > > Please, see the PR [2] for the suggested changes. > > > > [1]: > https://mail.python.org/pipermail/python-dev/2019-February/156272.html > > [2]: https://github.com/python/peps/pull/989 > > The text is available at > https://github.com/hroncok/peps/blob/pep394-2019/pep-0394.txt > > As a summary, I'll paste the rationale sections here: > > History of this PEP > =================== > > In 2011, the majority of distributions > aliased the ``python`` command to Python 2, but some started switching it > to > Python 3 ([5]_). As some of the former distributions did not provide a > ``python2`` command by default, there was previously no way for Python 2 > code > (or any code that invokes the Python 2 interpreter directly rather than via > ``sys.executable``) to reliably run on all Unix-like systems without > modification, as the ``python`` command would invoke the wrong interpreter > version on some systems, and the ``python2`` command would fail completely > on others. This PEP originally provided a very simple mechanism > to restore cross-platform support, with minimal additional work required > on the part of distribution maintainers. Simplified, the recommendation > was: > > 1. The ``python`` command was preferred for code compatible with both > Python 2 and 3 (since it was available on all systems, even those that > already aliased it to Python 3). > 2. The ``python`` command should always invoke Python 2 (to prevent > hard-to-diagnose errors when Python 2 code is run on Python 3). > 3. The ``python2`` and ``python3`` commands should be available to specify > the version explicitly. > > However, these recommendations implicitly assumed that Python 2 would > always be > available. As Python 2 is nearing its end of life in 2020 (PEP 373, PEP > 404), > distributions are making Python 2 optional or removing entirely. > This means either removing the ``python`` command or switching it to invoke > Python 3, invalidating respectively the first or second recommendation. > Also, some distributors decided that their users are better served by > ignoring the PEP's recommendations, making the PEP's supposedly > cross-platform recommendations on ``python`` and ``python2`` in shebangs > increasingly unreliable. > > > Current Rationale > ================= > > As of 2019, nearly all new systems include Python 3 and the ``python3`` > command. This makes the ``python3`` command the best general choice for > code that can run on either Python 3.x or 2.x, even though it is not > available everywhere. > > The recommendation is skewed toward current and future systems, leaving > behind “*old systems*” (like RHEL 6 or default Python installed on macOS). > On these systems, Python software is rarely updated and any recommendations > this PEP makes would likely be ignored. > > Also, since distributors often ignored recommendations the PEP gave > regarding the ``python`` command (for what they saw as legitimate special > needs), this PEP now gives them broad control over the command. > Correspondingly, users are advised to not use the ``python`` command > in cross-platform code. > Instead, this PEP specifies the expected behavior of the ``python3`` and > ``python2`` commands, which is not controversial. > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > https://mail.python.org/mailman/options/python-dev/guido%40python.org > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him/his **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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