[Python-Dev] Packaging documentation and packaging.pypi API (original) (raw)

Carl Meyer carl at oddbird.net
Wed Jun 20 19:09:25 CEST 2012

Hi Alexis,

On 06/20/2012 10:57 AM, Alexis Métaireau wrote:

Le mer. 20 juin 2012 18:45:23 CEST, Paul Moore a écrit :

Thanks - as you say, it's not so much the actual problem as the principle of what the packaging API offers that matters here. Although it does make a good point - to what extent do the packaging APIs draw on existing experience like that of pip? Given that tools like pip are used widely to address real requirements, it would seem foolish to not draw on that experience in designing a stdlib API. IIRC, pip relies nly onthe XML/RPC API to get information about the distributions from the cheeseshop. the code that's in packaging.pypi was built with the implementation in setuptools in mind, so we keep compatibility with setuptools "easyinstall".

No, this is not accurate. Pip's PackageFinder uses setuptools-compatible link-scraping, not the XMLRPC API, and it is the PackageFinder that is used to actually find distributions to install. I think PackageFinder is pretty much equivalent to what packaging.pypi is intended to do.

Pip does have a separate "search" command that uses the XMLRPC API - this is the only part of pip that uses XMLRPC. I consider this a bug in pip, because the results can be inconsistent with actual installation using PackageFinder, and "search" can't be used with mirrors or private indexes (unless they implement the XMLRPC API). The "search" command should just use PackageFinder instead.

That is, this leverages one question more on my side: was/is pip intended to be used as a library rather than as a tool / are there some people that are actually building tools on top of pip this way?

Pip's internal APIs are not documented, and they aren't the cleanest APIs ever, but some of them (particularly PackageFinder and InstallRequirement/RequirementSet) can be used without too much difficulty, and some people are using them. Not a lot of people, I don't think; I don't have hard numbers. I haven't seen much in the way of public reusable tools built atop pip, but I've talked with a few people building internal deployment tools that use pip as a library.

Carl

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