On Mon, Feb 18, 2019, 7:34 AM Matthias Klose <d...@ubuntu.com wrote: > On 16.02.19 00:15, Gregory P. Smith wrote: > > On Thu, Feb 14, 2019 at 9:29 AM Barry Warsaw <ba...@python.org> wrote: > > > >> On Feb 13, 2019, at 23:08, Matěj Cepl <mc...@cepl.eu> wrote: > >> > >>> Is this relevant to the discussion at hand? We are talking about > >>> the binary /usr/bin/python3 which will be surely be provided > >>> even by Python 4, won't it? > >> > >> Why would it be? Since this is all hypothetical anyway <wink>, I’d more > >> likely expect to only ship /usr/bin/python. > >> > > > > Because nobody can use 'python' and expect that to be anything but a > 2and3 > > compatible interpreter for the next 5+ years given we live in a world > where > > people routinely have a very real need to write #! lines that works with > > obsolete distributions. python3 implies >=3.x, thus python 4, 5, 6, > 2069, > > 3001, and 90210 should all have python3 point to them. realistically > > people will stop referring to python3 by 2069 so we could consider > removing > > the recommendation at that point. > > > > 2020 is not the end of use or end of importance for Python 2. It is > merely > > the end of bugfixes applied by python-dev. > > > > A thing I want to make sure we _don't_ do in the future is allow future > > pythonN binaries. python4, python90210, etc. those should never exist. > > python, python3, and pythonX.Y only. If we were ever to go back on our > > promise and create another world-breaking python version, it could get > its > > own canonical binary name. But we're specifically planning _not_ to make > > that mistake again. > > > > I suspect most of my opining below will be contentious to multiple people > > because I describe a state of the world that is at conflict with > decisions > > multiple independent distros have already made. Accept their mistakes > and > > move on past it to the hack in that case: > > > > A new "py" launcher isn't going to solve this problem - it is separate > and > > should be its own PEP as it has its own set of requirements and reasons > to > > be considered (especially on platforms with no concept of a #!). > Recommend > > "py" today-ish and nobody can rely on it for at least 10+ years in a wide > > support cross platform scripting type of situation because it won't be > > present on the obsolete or long term supported things that people have a > > need for such #!s to run on. > > > > Not our problem? Well, actually, it is. Matthias speaking for Debian > > suggesting they don't want to have "python" at all if it isn't a synonym > > for "python2" because it'll break software is... wrong. If software is > not > > 3 compatible and uses "python", it'll also break when python is python3. > > Just in a different manner. "python" should point to python3 when a > distro > > does not require python2 for its core. It should not _vary_ as to which > of > > 2.7 or 3.7 it will point to within a given stable distribution > (installing > > python2.7 should never suddenly redirect it back to python2). But > "python" > > itself should always exist when any python interpreter is core to the OS. > > That means if a distro no longer requires python2 as part of its > base/core > > but does require python3... "python" must point to "python3". If a > posixy > > OS no longer requires python at all (surely there are some by now?) the > > question of what python should point to when an OS distro supplied > optional > > python package gets installed is likely either "nothing at all" or > ">=3.x" > > but should never be decided as "2.7" (which sadly may be what macOS > does). > > There is no notion of a "core" for Debian. So "core" applies to the whole > distro, as long as there are python shebangs found. > > For Ubuntu, you don't have a python command on the default desktop > install, just > python3. Trying to invoke python, command-not-found tells you: > > $ python > > Command 'python' not found, but can be installed with: > > [...] > > You also have python3 installed, you can run 'python3' instead. > > That tells you which way to go. >
"Core" just means part of the minimal install, needed by startup scripts and the package manager perhaps. This would be a default install with no package groups selected or perhaps the netinst image for Debian. If packages in that set don't need a python interpreter, Debian is in great shape! :) > > Do we already have LTS _stable_ distributions making that mistake today? > > If so they've done something undesirable for the world at large and we're > > already screwed if that distro release is deemed important by masses of > > users: There is no way to write a *direct* #! line that works out of the > > box to launch a working latest version Python interpreter across all > > platforms. > > If you count the above example towards this "mistake", probably yes. But > there > is *no* way to have a sane way to have what you want. > Agreed. In the long run, expecting python 2 to exist is not sane. But given our pep394 text of "for the time being, all distributions *should* ensure that python, if installed, refers to the same target as python2," What Debian has done is still unfortunately encouraged by us. We've created a world where #! lines cannot be used to invoke an intentionally compatible script across a wide variety of platforms over time. But our decision to do that was the decision to have an incompatible release in the first place. Too late now. :)
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