On Wed, 19 Sep 2018 at 18:52, Donald Stufft <donald@stufft.io> wrote:
>
> On Sep 19, 2018, at 1:14 PM, Tzu-ping Chung <uranusjr@gmail.com> wrote:
>
> I feel the plan is quite solid. This however leaves us (who want a Python implementation and interface to do what pip does) in an interesting place. So I can tell there are a couple of principles:
>
> 1. Do not use pip internals
> 2. pip won’t be using either distlib or setuptools, so they might not match what pip does, in the long run
>
> Does this leaves us only one option left, to implement a library that matches what pip does (follows the standards), but is not pip? That feels quite counter-productive to me, but if it’s what things would be, I’d accept it.
>
> The next step (for me) in that case would then be to start working on that library. Since existing behaviours in setuptools and pip (including the part it uses distlib for) are likely to be standardised, I can rely on distlib for script creation, setuptools for some miscellaneous things (editable installs?), and pull (or reimplement) parts out of pip for others. Are there caveats I should look out?
>
>
> My general recommendation if you want a Python implementation/interface for something pip does, is:
>
> - Open an issue on the pip repository to document your intent and to make sure that there is nobody there who is against having that functionality split out. This might also give a chance for people with familiarity in that API to mention pain points that you can solve in a new API. We can also probably give you a good sense if the thing you want in a library is something that probably has multiple things that are dependent on getting split out first (for instance, if you said you wanted a library for installing wheels, we’d probably tell you that there is a dependency on PEP 425 tags, pip locations, maybe other that need resolved first) and also whether this is something that should have a PEP first or not. Getting some rough agreement on the plan to split X thing out before you start is overall a good thing.
>
> - Create or update a PEP if required, and get it into the provisional state.
>
> - Make the library, either as a PR to packaging or as it’s own independent library. If there are questions that come up while creating that library/PR that have to do with specific pip behaviors, go back to that original issue and ask for clarification etc. Ideally at some point you’ll open a PR on pip that uses the new library (my suggestion is to not bundle the library in the initial PR, and just import it normally so that the PR diff doesn’t include the full bundled library until there’s agreement on it). If there’s another tool (pipenv, whatever) that is looking to use that same functionality, open a WIP PR there too that switches it to using that. Use feedback and what you learn from trying to integrate in those libraries to influence back the design of the API itself.
>
> Creating a PEP and creating the library and the PRs can happen in parallel, but at least for pip if something deserves a PEP, we’re not going to merge a PR until that PEP is generally agreed on. However it can be supremely useful to have them all going at the same time, because you run into things that you didn’t really notice until you went to actually implement it.
>
> My other big suggestion would be to e careful about how much you bite off at one time. Pip’s internal code base is not the greatest, so pulling out smaller chunks at a time rather than trying to start right off pulling out a big topic is more likely to meet with success. Be cognizant of what the dependencies are for the feature you want to implement, because if it has dependencies, you’ll need to pull them out first before you can pull it out OR you’ll need to design the API to invert those dependencies so they get passed in instead.
>
> I personally would be happy to at a minimum participate on any issue where someone was trying to split out some functionality from pip into a re-usable library if not follow the develop of that library directly to help guide it more closely. My hope for pip is that it ends up being the glue around a bunch of these libraries, and that it doesn’t implement most of the stuff itself anymore.

I basically agree with everything Donald said, and I'd also be happy
to support any work along these lines. If you're looking for a place
to start, I'd strongly recommend some of the foundational areas -
something like pip.locations (I know there are others who have
expressed an interest in this PI being exposed), or pep425tags which
has the advantage of already having a standard, or something at that
level. Starting with something at the level of the finder or the
installer is likely to be way too much to start with, even if it feels
like it would be more directly useful to you.

Paul
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