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

Brett Cannon brett at python.org
Fri Feb 15 17:35:44 EST 2019

On Thu, Feb 14, 2019 at 10:21 AM Gustavo Carneiro <gjcarneiro at gmail.com>

> On Thu, 14 Feb 2019 at 15:52, Victor Stinner <vstinner at redhat.com> wrote:
>> Le jeu. 14 févr. 2019 à 14:38, Matthias Klose <doko at ubuntu.com> a écrit :
>> > Debian's concern about pointing python to python3 is that it will break
>> software
>> > after an upgrade.  The current state seems is still the same that
>> Debian doesn't
>> > want to ship a python symlink after the Python2 removal.
>> The other safer alternative is to start to provide "py" launcher on
>> Unix as well. Since it's something new, it's perfectly fine to decide
>> from the start to make it point to the latest Python version by
>> default.
> While I like very much the idea of having `py` as command, does it really
> need to be a wrapper command?  Why can't it simply be a symlink?
>     /usr/bin/py -> /usr/bin/python3

Because that is not guaranteed to be the *latest* version of Python 3, just
the *last* version installed or the *first* one that happens to be on PATH.

> I worry about (1) startup time overhead of starting another process,

It's being implemented in Rust, uses execv(), etc. The initial design is
such that it is meant to minimize overhead such that you should worry more
about what you import at startup than using the Python launcher if you're
that concerned with startup performance. :) But honestly, you don't *have*
to use the launcher; it's just for convenience.

> (2) added complexity of learning about py's additional command-line
> options, we don't really need them, imho.

There's only 2 more and they only work in the first position, so the
cognitive overhead is extremely low.

In my experience after using 'py' on Windows I consistently miss it on UNIX
now, so to me there is enough of a benefit that I will continue to chip
away at the project until it's done regardless of whether anyone else uses
it. :)


>> Victor
>> --
>> Night gathers, and now my watch begins. It shall not end until my death.
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> --
> Gustavo J. A. M. Carneiro
> Gambit Research
> "The universe is always one step beyond logic." -- Frank Herbert
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