[Python-Dev] PEP 394 - Clarification of what "python" command should invoke

Donald Stufft donald at stufft.io
Fri Sep 19 10:44:26 CEST 2014

> On Sep 19, 2014, at 3:31 AM, Bohuslav Kabrda <bkabrda at redhat.com> wrote:
> Hi,
> as Fedora is getting closer to having python3 as a default, I'm being more and more asked by Fedora users/contributors what'll "/usr/bin/python" invoke when we achieve this (Fedora 22 hopefully). So I was rereading PEP 394 and I think I need a small clarification regarding two points in the PEP:
> - "for the time being, all distributions should ensure that python refers to the same target as python2."
> - "Similarly, the more general python command should be installed whenever any version of Python is installed and should invoke the same version of Python as either python2 or python3."
> The important word in the second point is, I think, *whenever*. Trying to apply these two points to Fedora 22 situation, I can think of several approaches:
> - /usr/bin/python will always point to python3 (seems to go against the first mentioned PEP recommendation)
> - /usr/bin/python will always point to python2 (seems to go against the second mentioned PEP recommendation, there is no /usr/bin/python if python2 is not installed)
> - /usr/bin/python will point to python3 if python2 is not installed, else it will point to python2 (inconsistent; also the user doesn't know he's running and what libraries he'll be able to import - the system can have different sets of python2-* and python3-* extension modules installed)
> - there will be no /usr/bin/python (goes against PEP and seems just wrong)
> I'd really appreciate upstream guidance and perhaps a PEP clarification for distributions that ship both python2 and python3, but can live without python2 (and are not Arch :)).
> Thanks a lot!

I don’t know for a fact, but I assume that as long as Python 2.x is installed by default than ``python`` should point to ``python2``. If Python 3.x is the default version and Python 2.x is the “optional” version than I think personally it makes sense to switch eventually. Maybe not immediately to give people time to update though?

Donald Stufft
PGP: 7C6B 7C5D 5E2B 6356 A926 F04F 6E3C BCE9 3372 DCFA

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