On Mon, 2017-07-31 at 00:02 +1000, Nick Coghlan wrote:
On 30 July 2017 at 07:57, Björn Persson <Bjorn(a)xn--rombobjrn-67a.se>
> Mathieu Bridon <bochecha(a)daitauha.fr> wrote:
> > To be honest, given how much energy is spent on this migration
> > for a very low gain, it makes me feel like having an unversioned
> > "python" (whether as package or executable names) was a mistake
> > we should let disappear with Python 2.
> I agree.
> From an emotional point of view I fully understand the Python
> folks' desire to have "Python" mean Python 3, and that's fine in
> marketing contexts such as websites.
While I'm a CPython core dev in addition to being a RHEL developer,
it's mainly the latter role that leads me to consider the status quo
in Fedora as being rather problematic :)
> But filenames and package names are technical
> identifiers. They must be chosen so that they'll fulfil their
> functions, and with consideration for forward and backward
Right. Unfortunately, the folks saying "just use /usr/bin/python3 in
your shebang lines" are choosing to ignore systems that don't have,
and *aren't going to get* a Python 3 installation. Even if Red Hat
were to start making a native Python 3 stack available, there would
still be an awful lot of EL6 and EL7 systems around where that stack
isn't going to be installed.
Sure, but nobody is telling everybody to use /usr/bin/python3 in their
I started this subthread saying everybody should just use the versioned
executable in their shebang line. Whether that's Python 2 or 3 depends
on what's available on their system and what they are targetting.
So that's effectively a hard design constraint for me: folks
targeting EL6 and EL7 *are* going to have to use "/usr/bin/python" in
their shebang lines (since they can't even assume "/usr/bin/python2"
will be present,
I see /usr/bin/python2 in the EL7 spec file:
I'm pretty sure I had /usr/bin/python2 back in the days when I was
using EL6. (but I have no way to check that now)
let alone "/usr/bin/python3"), so I have to assume that
Red Hat's customers to change all their Python shebang lines to
require Python 3" isn't one of the design options I have available to
And again, nobody in this subthread suggested moving things to Python
That means the only degrees of freedom I/we potentially have are
related to what "/usr/bin/python" means in Fedora. The status quo is
that by default such scripts simply break, and if you want them to
work, you have to install the full Python 2.7 stack.
Which, again, is what happens for other shebang lines like /usr/bin/zsh
Having to install the stack needed by your custom-built tools seem like
a perfectly normal thing to me.
If you want to do anything else, you have to resort to creating
symlinks manually, and as soon as you do, your system is in an
unsupported configuration, so if it breaks, any bugs you file are
just going to be closed as "not a bug".
Accordingly, my proposal is that we support *3* admin selectable
That seems like a recipe for confusion. How does one know what
/usr/bin/python actually is if it can change from one machine to
> Providing an unversioned "python" serves only to lure
> programmers into using it where they should use a versioned name.
My aim is for folks to start thinking of a "/usr/bin/python" shebang
as being akin to writing "/bin/sh" instead of "/bin/bash": as the
author of the script, by deciding not to explicitly qualify your
shebang line you're saying "I'm not writing in either Python 2 *or*
Python 3, I'm writing in the hybrid subset of both of them". There
aren't many good reasons for a script in a distro package to do that
(they should just depend on the stack they want), but there are
plenty of good reasons for multi-distro scripts to be written that
As time goes by, I'd expect the meaning of the unqualified variant to
shift slightly such that "/usr/bin/python" is taken to mean "written
in the oldest Python dialect that is still actively supported by
upstream and/or commercial vendors (or potentially even older than
that)" while "/usr/bin/python3" retains its current meaning of "run
in the default Python 3 stack" (with the two links thus becoming
functionally equivalent for systems that only have one Python stack
I can't see admins testing their scripts on multiple Python version. A
lot of us Python developers already don't want to bother with that, and
just target one or another. :) (or something like Python >= 3.4)
In case I wasn't clear, my proposal when I began this subthread was:
* have the versioned /usr/bin/pythonX for each major version of Python
* /usr/bin/python will remain a symlink to /usr/bin/python2 forever, as
long as we decide to keep a Python 2 stack in Fedora, and after that
it would just disappear;
This means that existing scripts using /usr/bin/python as a shebang
will keep working as long as we have Python 2 in Fedora, we won't break
them by switching what Python version is pointed to by the symlink.
It also means people wanting to move their script to Python 3 will just
opt-in to it by using the /usr/bin/python3 shebang, after which their
script will always run on Python 3.
When Python 4 comes in, we'd introduce /usr/bin/python4 and people
would have their script keep working on Python 3, until they are ready
to port them and opt-in to Python 4 by switching their shebang line.
After all, "explicit is better than implicit". ;)