On Fri, 5 Jul 2019 at 21:33, Steve Dower <report@bugs.python.org> wrote:
> Yeah. We probably need to be clear about which approaches are actually supported and which ones are not.
>
> Ultimately though, I think this is a situation where the breakage is forced upon us (by the operating system), and so fixing the behaviour of our built-in functionality pretty clearly outweight preserving the assumptions made by third-parties (especially since those assumptions are going to break).

Well, given that this is an issue specific to the store distribution
of Python, I'd say that it's the release of the store build that
forces it on us, not the OS, and releasing the store build was our
choice, so if we did so with the store build not meeting existing
implicit (i.e. undocumented, I agree) contracts, then we made that
choice. I think it was the right choice, because the store
distribution is a huge plus, but I do think we should be cautious
about impacting the existing user base simply because of a very new,
and explicitly documented as "still experimental" build. (Yes, I'm
still a bit sore about the hassle involved in getting virtualenv to
work - although the final resolution to that issue was IMO clean and a
huge improvement on the previous status quo, so I'm not *really* sore
:-))

> > IMO, we should bite the bullet here and actually document the
> > interfaces involved in virtual environments, so that tools have a
> > stable contract to work with. That way we'd limit the need for people
> > to rely on undocumented behaviour in the first place.
>
> I feel like I've made this argument before, but I suspect if we'd documented them prior to this change, we'd now have no choice but to remain broken.

Hardly. We would simply have had to document the changed behaviour and
follow our existing transition/compatibility processes. Documenting
things doesn't lock them in stone, it just requires us to give due
consideration to our users when we change things. Conversely, *not*
documenting things makes it easier for us to change things, at the
cost of not giving users supported ways to do certain things that they
may still need to do.

> The interfaces that should be documented are "-m venv", venv.VenvBuilder, and the activation scripts, none of which had to change. But if we start making promises about how "python.exe" actually behaves in a venv then we're going to paint ourselves into a corner very quickly - the venv approach just doesn't scale well to the range of systems people use. (Obligatory mention that PEP 582 would have avoided this whole mess by not requiring us to duplicate python.exe anywhere. But it just wasn't meant to be.)

I assume you're missing my key point here (not unlikely, as I didn't
state it explicitly - I guess I'm relying on undocumented information
myself ;-)). The point here is that venv doesn't exist in a vacuum,
before it existed, virtualenv was the standard way to produce virtual
environments. And because neither virtualenv nor venv document any of
their internal details, they are plagued with incompatibilities, and
work badly together. As a result, tools like pipenv, or pew, or pipx,
can't support both but end up picking just one - and because of
backward compatibility requirements, they pick virtualenv, which has
significantly hindered adoption of venv, which is (for hopefully
obvious reasons) a substantially more robust solution.

It may be that it's just too late to worry about this, and we should
simply accept that tools will be dropping Python 2 support very soon
now, at which point there's no real reason to continue using
virtualenv (apart from no-one having the time to make the change, but
if virtualenv adopts venv as its internal mechanism we can get around
that). But personally, I'd rather not rely on an assumption like that,
just yet (maybe in 3.9?).

(Side issue, I don't really see the relevance of PEP 582 here, as I
don't think it's something that tools like tox and pipenv could
replace virtual environments with - but maybe I'm wrong, if so the
arguments for PEP 582 didn't really get that point across).