[Python-Dev] Another update for PEP 394 -- The "python" Command on Unix-Like Systems

[Antoine Pitrou]

On Wed, 13 Feb 2019 17:18:15 +0100
Petr Viktorin <encukou at gmail.com> wrote:
> On 2/13/19 4:46 PM, Antoine Pitrou wrote:
> > On Wed, 13 Feb 2019 16:24:48 +0100
> > Petr Viktorin <encukou at gmail.com> wrote:  
> >> PEP 394 says:
> >>  
> >>   > This recommendation will be periodically reviewed over the next few
> >>   > years, and updated when the core development team judges it
> >>   > appropriate. As a point of reference, regular maintenance releases
> >>   > for the Python 2.7 series will continue until at least 2020.  
> >>
> >> I think it's time for another review.
> >> I'm especially worried about the implication of these:
> >>
> >> - If the `python` command is installed, it should invoke the same
> >>     version of Python as the `python2` command
> >> - scripts that are deliberately written to be source compatible
> >>     with both Python 2.x and 3.x [...] may continue to use `python` on
> >>     their shebang line.
> >>
> >> So, to support scripts that adhere to the recommendation, Python 2
> >> needs to be installed :(  
> > 
> > I think PEP 394 should acknowledge that there are now years of
> > established usage of `python` as Python 3 for many conda users.  
> 
> The intention is that Conda environments are treated the same as venv 
> environments, i.e.:
> 
> When a virtual environment (created by the PEP 405 venv package or a 
> similar tool) is active, the python command should refer to the virtual 
> environment's interpreter. In other words, activating a virtual 
> environment counts as deliberate user action to change the default 
> python interpreter.

Anaconda is often used as providing, not only virtual environments, but
the "main" user Python.  At least it certainly is so on Windows and
macOS, but I'm sure it is used like that as well on Linux, especially on
ancient distributions such as RHEL 6 or Ubuntu 14.04.

In any case, the fact that many people are used to "python" pointing to
Python 3 is IMHO an important data point.

Regards

Antoine.