[Distutils] Why I like eggs (or similar mechanisms) and my thoughts on future of buildout

[Paul Moore]

On 20 August 2016 at 22:31, Nathaniel Smith <njs at pobox.com> wrote:
> Wheels are a pretty simple and straightforward format. They've got some
> metadata, and then the are a set of directories with labels attached: "this
> directory needs to go on sys.path", "this directory has scripts that should
> have shebang fixups applied and then go on $PATH", etc. (The spec is not
> long: https://www.python.org/dev/peps/pep-0427/)
>
> My first guess at how buildout could handle wheels elegantly would be:
>
> - we have one piece of code that abstracts the operation of "please give me
> a wheel for package X version Y that works on this system".

This can be abstracted at the moment as "pip wheel <requirement>".
That will deliver a wheel to the current directory which is exactly
what is described above. It probably doesn't meet buildout's
repeatability requirements (as it could invoke a build step if there's
no published wheel, and build steps can do anything they like -
--only-binary would be a way to avoid that, at the cost of failing if
a project didn't publish a wheel) but it would likely work as a
prototype.

I don't think there's anything inherent in buildout's isolation model
of using sys.path entries for each dependency, that is incompatible
with pip/wheels. If buildout unpacks eggs, it can do the same with
wheels. If it uses zipped eggs, then it can *probably* do the same
with wheels, although there's no "zip safe" mechanism to declare a
wheel as safe for this use.

Paul