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

[Paul Moore]

On 17 November 2017 at 01:57, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 17 November 2017 at 05:15, Chris Barker <chris.barker at noaa.gov> wrote:
>>
>> On Wed, Nov 15, 2017 at 11:07 AM, Steve Dower <steve.dower at python.org>
>> wrote:
>>>
>>> If you write such a PEP, please also research and write up the issues
>>> with modifying PATH on Windows (they're largely scattered throughout
>>> bugs.p.o and earlier discussions on python-dev).
>>
>>
>> Is anyone proposing doing anything new with that? (other than changing the
>> default)
>>
>>> My preferred solution for this is to rename "py.exe" to "python.exe"
>>
>>
>> I was going to propose that in this thread, but then thought: "there has
>> GOT to be a reason why that reall obvious solution wan't done in the first
>> place", and didn't have time to go back and research it.
>
>
> As far as I recall, the arguments against it are:
>
> - wanting the regular executable and the launcher to be able to coexist in
> the same build target directory
> - not wanting the regular python executable to prevent access to the
> launcher at a shell prompt
> - not wanting the launcher at a shell prompt to prevent access to the
> regular executable at a shell prompt
>
> However, https://www.python.org/dev/peps/pep-0397/ doesn't spell those out,
> it just states what the launcher's name will be, and emphasises that the
> main purpose is to provide a sensible target for file associations after the
> "always use the most recently installed version" assumption broke down:
> https://www.python.org/dev/peps/pep-0397/#rationale
>
> Addressing them now:
>
> * as long as the extra hard links are only generated at install time, there
> also won't be any problems with build directory name conflicts.
> * the launcher will always be available a `py`, regardless of the current
> PATH
> * PATH in a venv will still put the regular python executable ahead of the
> launcher

Note that if I *do* get round to working on this, my primary intention
will be to propose altering the launcher to allow it to be used under
different names, as described by Steve. However, I won't initially be
proposing that we add any additional links to the launcher by default,
leaving that for users to do manually, and/or for later revisions of
the PEP (or further PEPs) to propose this.

Reasons:

1. The launcher is typically in C:\Windows, which has a very high
priority on PATH, so getting the environment right will be tricky.
2. I don't have any real experience with the installer.
3. Backporting this change, or dealing with older versions of Python
that don't include the new launcher, is a complicated question.

I'd rather keep the initial PEP restricted to the simple behaviour
change. It's possible that the behaviour change may not even need a
PEP, but I think it'd be better to have one. The "how do we use the
new behaviour in the installers" question is likely to be much more
controversial...

Paul

PS This (particularly the replacement of python.exe) is almost
certainly too late for 3.7, so it's not as if there's a rush to answer
all the questions at once :-)