On 02/03/11 08:06, Guido van Rossum wrote:
On Tue, Mar 1, 2011 at 1:26 PM, Eric Smith<e...@trueblade.com> wrote:
On 3/1/2011 4:19 PM, Kerrick Staley wrote:
Hello,
There is a need for the default Python2 install to place a symlink at
/usr/bin/python2 that points to /usr/bin/python, or for the
documentation to recommend that packagers ensure that python2 is
defined. Also, all documentation should be changed to recommend that
"#!/usr/bin/env python2" be used as the shebang for Python 2 scripts.
This is needed because some distributions (Arch Linux, in particular),
point /usr/bin/python to /usr/bin/python3, while others (including
Slackware, Debian, and the BSDs, probably more) do not even define the
python2 command. This means that a script has no way of achieving
cross-platform compatibility. The point at which many distributions
begin to alias /usr/bin/python to /usr/bin/python3 is due soon, and for
the next couple of years, it would be best to use a python2 or python3
shebang in all scripts, making no assumptions about plain python, which
should only be invoked interactively. This email from about 3 years ago
seems relevant: :
http://mail.python.org/pipermail/python-3000/2008-March/012421.html
Again, this issue needs to be addressed by the Python developers
themselves so that different *nix distributions will handle it
consistently, allowing Python scripts to continue to be cross-platform.
I believe we agreed at the language summit last year (or maybe even the year
before) that "python" would always be python2.x, and "python3" would be
python3.x.
And by "always" we indeed meant forever. To do otherwise would break scripts
even many, many years from now.
Unfortunately distros are not following these guidelines. As long as
we still have the pythonX.Y links I think it's better to have
"python2", "python3" and "python" than total anarchy.
This was brought up when Arch Linux switched /usr/bin/python to point a
python3 around six months ago, and at the time no-one could actually
recall the decision to always point /usr/bin/python at python2 forever.
In fact, the only decision that was clearly made (and acted on) was
that "make install" for python3 would install /usr/bin/python3.
e.g. http://www.mail-archive.com/python-dev@python.org/msg53204.html
But if that decision was made, it was not documented anywhere that I can
find, so effectively was a non-decision...
Deciding that /usr/bin/python going to always point at python2 just
makes me think that python3 is always going to be a second class
citizen. Eventually python-2.7 will be long gone and it would seem
wrong for people will still be using "python3" to run their scripts once
python-3.xx is the primary python version.
So a transition is going to need to be made here at some stage. Most
distributions have been providing the /usr/bin/python2 symlink for a
long time, with Debian being the notable exception. I think adding such
a symlink is in the realm of what distribution packagers can choose to
do on their own, but having it done automatically for python-2.7 would
also be of benefit.
Allan
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