[Python-ideas] Looking for input to help with the pip situation

[Paul Moore]

On 20 November 2017 at 21:59, Chris Barker <chris.barker at noaa.gov> wrote:
> I don't understand any of this enough to have an opinion, so while I'd like
> to see py.exe be renamed python.exe, let's not let "the perfect be the enemy
> of good enough". So, if someone can make the case that they can restructure
> the whole py.exe / python.exe thing nicely in a way that will work, AND
> write the code to do it fairly quickly, then great!

I'm happy enough to modify the py.exe code to base its behaviour on
the name it's called with, as Steve suggested. I'm not sure if that
would require a PEP, but I'm willing to do one if it's felt that there
is a need. It should be possible to get that change in for 3.7. I
don't know what would be the best approach for adding copies/links of
the launcher under other names, though. And I don't have any
experience with the tools we use to build the installer, so that would
be for someone else. That part probably *would* need a PEP, and it may
well be controversial enough that getting agreement in time for 3.7
(i.e. in the next 2 months or so) will be challenging.

I think the launcher change is worthwhile in its own right. Even if we
don't install any aliases by default, users will be able to manually
add them. (And someone could write a 3rd party tool to manage creation
of such aliases, making that capability available to users who don't
have the necessary skills themselves).

> Otherwise, let's at least get a python3.exe into 3.7 -- and ideally into
> updates to 3.5, 3.6, and (python2.exe in this case, 2.7)

It's not going to be acceptable for 3.5, as that is now in security
fix only mode. I'm not certain it's even acceptable for bugfix-only
releases. It's a backward incompatible change (3.6.3 has no
python3.exe but python 3.6.4 does) but maybe an acceptable one - we'd
need feedback from the 3.6 and 2.7 release managers on that.

Also, I'm assuming here you mean "create a copy of python.exe called
python3.exe". If we do that, we risk making it harder to later switch
to making "python3.exe" a link to the launcher - for the same reason
that making "python.exe" be an alternative name for the launcher is
problematic right now.

> And maybe make "add to PATH" be the default in the installer.

I'm not willing to contradict Steve on this one. There are too many
not-uncommon cases that we could mess up badly here. It's the right
choice for "make new users' experience as easy as possible", but if we
do this at the cost of making the experience of people upgrading to
3.7 (possibly by installing 3.7 to gradually switch over, or starting
their migration from 2.7 with 3.7) unpleasant, then we risk getting
bad publicity for the 3.7 release.

The history of how we added Python to PATH across various versions is
messy and inconsistent. Add to that other distributions (Anaconda,
ActiveState) making different choices and adding yet more
inconsistency, means that anyone who *isn't* a brand new user probably
already has a tweaked, and likely fragile, setup. We're not doing them
any favours by adding another new behaviour. (And enabling "Add to
PATH" in 3.7 *would* be a new behaviour - I don't think we've enabled
add to path by default in any version since we switched to per-user
installs as the default).

We need *another* solution here. Not just variations on the existing
mess. That's why I like Steve's suggestion of making the launcher into
the canonical entry point. It's not easy, but at least it stands a
chance of breaking out of the cycle we're currently in, of switching
back and forth between "add to PATH" and "don't add to PATH".

> Those are quick and simple to do, result in little disruption, and make the
> whole cross-platform thing more manageable.

They aren't that simple. I've already discussed "add to PATH". And if
we add python3.exe, we have to consider questions like will venv be
modified to include it in virtual environments? Will virtualenv? If
not, will "python3" run the system Python rather than the current
virtualenv? That's just as much a problem for the option of having
python3 be an alias for the launcher, of course - but my point here is
you have to think about questions like this even for your "simple"
approach.

I just don't think there *is* a quick and simple solution here. So
better not to rush into a solution that isn't fully thought through,
IMO. "Although never is often better than *right* now" is the relevant
Zen here, not "Now is better than never" (nobody's suggesting we
*never* fix this).

> BTW -- does pip install a "pip3" on Windows?

No. Just "pip.exe".

Paul