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From: Geoffrey Thomas <geofft@ldpreload.com>
Newsgroups: linux.debian.maint.python
Subject: Re: MBF for deprecating Python2 usage
Date: Tue, 08 Aug 2017 04:10:02 +0200
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On Tue, 8 Aug 2017, Ben Finney wrote:

> The issue is: Invoking =E2=80=98python=E2=80=99 today gets an interperete=
r, Python 2,
> that will work with some code and not others. It should not tomorrow
> invoke an incompatible interpreter without *knowing* that the vast
> majority of scripts in the wild no longer expect Python 2 to come from
> that command.
>
> That day might never come, in which case the =E2=80=98python=E2=80=99 com=
mand will
> forever mean Python 2. That is, I'm saying, better than breaking that
> command in the near or medium future.
>
> I'm saying it's a bad idea for =E2=80=98python=E2=80=99 tomorrow to get a=
n incompatible
> intepreter that won't run the same Python code. That interpreter is
> named =E2=80=98python3=E2=80=99 and should never be installed as =E2=80=
=98python=E2=80=99, because
> =E2=80=98python=E2=80=99 is a command that many scripts expect to invoke =
Python 2.

This conflates the role of the interactive Python interpreter (which is=20
what Diane was referring to) and a script interpreter. #!/usr/bin/python=20
and `python -c` are ABI referring to Python 2, yes, and can't start=20
running Python 3 any more than /lib/libc.so.5 can start being glibc. But=20
there's no reason this should prevent typing "python" from giving you a=20
Python 3 interpreter.

Since I think it hasn't been linked recently on this list, I'll re-link=20
this project, which separates the two roles:

     https://github.com/geofft/pythonmux
     https://ldpreload.com/blog/usr-bin-python-23

Keep in mind that we do intend to break the ability for /usr/bin/python to=
=20
run Python 2 code in less than three years (unless we're interested in=20
providing security support for Python 2 when it's dead upstream, which I=20
hope nobody wants to do). We will not indefinitely provide a=20
/usr/bin/python that runs Python 2; we probably will do so for at most one=
=20
more stable release.

The only question is whether it should break by giving you an error=20
message (either ENOENT or something printed on stderr), or break by trying=
=20
to run the code as Python 3.

--=20
Geoffrey Thomas
https://ldpreload.com
geofft@ldpreload.com
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