[Distutils] Installed Extras Metadata

[Nick Coghlan]

On 27 January 2018 at 03:44, Pradyun Gedam <pradyunsg at gmail.com> wrote:

>
> On Fri, 26 Jan 2018 at 23:10 Pradyun Gedam <pradyunsg at gmail.com> wrote:
>
>> Resending coz I clicked the wrong button.
>>
>> On Fri, 26 Jan 2018 at 22:16 Paul Moore <p.f.moore at gmail.com> wrote:
>>
>>> On 26 January 2018 at 16:07, Pradyun Gedam <pradyunsg at gmail.com> wrote:
>>> >> Is there any other place where current functionality needs this
>>> >> information, *apart* from pip check? Are there any proposed additional
>>> >> features that might need it?
>>> >
>>> > Yes. I currently have a branch where during pip install, after the
>>> packages
>>> > to be installed are selected, it does a pip check on what would be the
>>> > installed packages if the installation is successful. This would mean
>>> that
>>> > if we do select an incompatible version for installation, pip install
>>> would
>>> > be able to print a warning.
>>>
>>> I'd rather see us get a proper solver that would mean this should
>>> never happen :-)
>>
>>
>>>
>> Yep, I am working on that. This is more of a short-term thing that I'm
>> thinking of, just in case the proper solver isn't ready in time for pip 10.
>> :)
>>
>
> And the resolver will need this extras-installed metadata as well.
>

`pipenv lock` could likely also benefit from this (although in our case we
can also check `Pipfile` to see if any extras have been explicitly
requested).

>From the point of view of post-install-metadata-readability, something else
we don't currently record is the *result* of environment marker expressions
at the time of installation.

This means that there's no particularly straightforward way to check the
portability of an entire virtual environment, whereas if we recorded the
environment marker expressions and their outcomes somewhere, then we'd be
able to extract a consolidated list of the environmental expectations for
that venv.

Ideally, we'd also be able to record somewhere which dependencies had been
satisfied from *outside* the venv, again with the goal of extracting a
consolidated list of the expectations the venv is placing on the host
Python environment.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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