[Distutils] command line versus python API for build system abstraction (was Re: build system abstraction PEP)

[Robert Collins]

On 11 November 2015 at 18:53, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 11 November 2015 at 08:44, Nathaniel Smith <njs at pobox.com> wrote:
>> On Mon, Nov 9, 2015 at 6:11 PM, Robert Collins
>> <robertc at robertcollins.net> wrote:
>>> On 10 November 2015 at 15:03, Nathaniel Smith <njs at pobox.com> wrote:
>> Similarly, we still have to specify how what the different operations
>> are, what arguments they take, how they signal errors, etc. The point
>> though is this specification will be shorter and simpler if we're
>> specifying Python APIs than if we're specifying IPC APIs, because with
>> a Python API we get to assume the existence of things like data
>> structures and kwargs and exceptions and return values instead of
>> having to build them from scratch.
>
> I think the potentially improved quality of error handling arising
> from a Python API based approach is well worth taking into account.
> When the backend interface is CLI based, you're limited to:
>
> 1. The return code
> 2. Typically unstructured stderr output
>
> This isn't like HTTP+JSON, where there's an existing rich suite of
> well-defined error codes to use, and an ability to readily include
> error details in the reply payload.
>
> The other thing is that if the core interface is Python API based,
> then if no hook is specified, there can be a default provider in pip
> that knows how to invoke the setup.py CLI (or perhaps even implements
> looking up the CLI to invoke from the source tree metadata).

Its richer, which is both a positive and a negative. I appreciate the
arguments, but I'm not convinced at this point.

pip is going to be invoking a CLI *no matter what*. Thats a hard
requirement unless Python's very fundamental import behaviour changes.
Slapping a Python API on things is lipstick on a pig here IMO: we're
going to have to downgrade any richer interface; and by specifying the
actual LCD as the interface it is then amenable to direct exploration
by users without them having to reverse engineer an undocumented thunk
within pip.

-Rob

-- 
Robert Collins <rbtcollins at hp.com>
Distinguished Technologist
HP Converged Cloud